diff --git a/1-js/01-getting-started/1-intro/article.md b/1-js/01-getting-started/1-intro/article.md
index 4be1d0bcd..2b561d771 100644
--- a/1-js/01-getting-started/1-intro/article.md
+++ b/1-js/01-getting-started/1-intro/article.md
@@ -6,7 +6,11 @@ Vamos ver o que há de tão especial no JavaScript, o que podemos fazer com ele,
 
 *JavaScript* foi inicialmente criado para *" tornar páginas web vivas "*.
 
+<<<<<<< HEAD
 Os programas nesta linguagem são chamados de *scripts*. Eles podem ser escritos diretamente no HTML de uma página web e executados automaticamente quando a página é carregada.
+=======
+The programs in this language are called *scripts*. They can be written right in a web page's HTML and run automatically as the page loads.
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 
 Os scripts são fornecidos e executados como texto puro. Eles não precisam de preparação ou compilação especial para serem executados.
 
@@ -70,7 +74,11 @@ Exemplos de tais restrições incluem:
    Existem maneiras de interagir com a câmera / microfone e outros dispositivos, mas eles exigem permissão explícita do usuário. Assim, uma página habilitada para JavaScript pode não habilmente habilitar uma câmera web, observar os arredores e enviar as informações para a [NSA](https://pt.wikipedia.org/wiki/Ag%C3%AAncia_de_Seguran%C3%A7a_Nacional).
 - Diferentes abas/janelas geralmente não se conhecem mutuamente. Às vezes sim, por exemplo, quando uma janela usa JavaScript para abrir a outra. Mas mesmo neste caso, JavaScript de uma página pode não acessar a outra se eles vierem de sites diferentes (de um domínio, protocolo ou porta diferente).
 
+<<<<<<< HEAD
     Isso é chamado de "Política de mesma origem ". Para contornar isso, *ambas as páginas* devem conter um código JavaScript especial que lida com a troca de dados.
+=======
+    This is called the "Same Origin Policy". To work around that, *both pages* must agree for data exchange and contain a special JavaScript code that handles it. We'll cover that in the tutorial.
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 
     Essa limitação é, novamente, para a segurança do usuário. Uma página de `http://umsitequalquer.com.br` que um usuário abriu não deve poder alcançar uma outra aba do navegador com a URL `http://gmail.com` e roubar a informação de lá.
 - O JavaScript pode se comunicar facilmente pela rede com o servidor de onde a página atual veio. Mas sua capacidade de receber dados de outros sites / domínios é prejudicada. Embora possível, requer acordo explícito (expresso em cabeçalhos HTTP) do lado remoto. Mais uma vez, isso é uma limitação de segurança.
diff --git a/1-js/02-first-steps/01-hello-world/article.md b/1-js/02-first-steps/01-hello-world/article.md
index 6a5794e08..386598bec 100644
--- a/1-js/02-first-steps/01-hello-world/article.md
+++ b/1-js/02-first-steps/01-hello-world/article.md
@@ -1,6 +1,10 @@
 # Olá, mundo!
 
+<<<<<<< HEAD
 O tutorial que você está lendo é sobre a core do JavaScript, que é independente de plataforma. Mais tarde, você vai aprender sobre Node.js e outras plataformas que o usam.
+=======
+This part of the tutorial is about core JavaScript, the language itself. Later on, you'll learn about Node.js and other platforms that use it.
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 
 Mas precisamos de um ambiente de trabalho para rodar nossos scripts e, como esse livro está online, o navegador é uma boa escolha. Vamos manter a quantidade de comandos específicos do navegador (como `alert`) no mínimo para que você não gaste tempo com eles se você planeja se concentrar em outro ambiente (como Node.js). Vamos focar em JavaScript no navegador na [próxima parte](/ui) do tutorial.
 
@@ -45,8 +49,13 @@ A tag `<script>` contém código JavaScript que é executado automaticamente qua
 
 A tag `<script>` tem alguns atributos que raramente são usados hoje em dia, mas que ainda podem ser encontrados em códigos antigos:
 
+<<<<<<< HEAD
 O atributo `type`: <code>&lt;script <u>type</u>=...&gt;</code>
 : O antigo padrão HTML, HTML4, requeria um script para ter um `type`. Normalmente era `type="text/javascript"`. Não é mais necessário. Além disso, o moderno padrão HTML, HTML5, mudou totalmente o significado deste atributo. Agora, ele pode ser usado para módulos JavaScript. Mas esse é um tópico avançado; vamos falar sobre módulos em outra parte do tutorial. 
+=======
+The `type` attribute: <code>&lt;script <u>type</u>=...&gt;</code>
+: The old HTML standard, HTML4, required a script to have a `type`. Usually it was `type="text/javascript"`. It's not required anymore. Also, the modern HTML standard, HTML5, totally changed the meaning of this attribute. Now, it can be used for JavaScript modules. But that's an advanced topic; we'll talk about modules in another part of the tutorial.
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 
 O atributo `language`: <code>&lt;script <u>language</u>=...&gt;</code>
 : Este atributo foi criado para mostrar o idioma do script. Este atributo não faz mais sentido porque JavaScript é a linguagem padrão. Não há necessidade de usá-lo.
diff --git a/1-js/02-first-steps/04-variables/article.md b/1-js/02-first-steps/04-variables/article.md
index 827a06d85..6832de2cd 100644
--- a/1-js/02-first-steps/04-variables/article.md
+++ b/1-js/02-first-steps/04-variables/article.md
@@ -135,8 +135,13 @@ alert(hello); // Olá Mundo!
 alert(message); // Olá Mundo!
 ```
 
+<<<<<<< HEAD
 ```smart header="Linguagens funcionais"
 É interessante notar que linguagens de programação [funcional](https://en.wikipedia.org/wiki/Functional_programming), como [Scala](http://www.scala-lang.org/) or [Erlang](http://www.erlang.org/), proibem a modificação de valores de variáveis.
+=======
+```smart header="Functional languages"
+It's interesting to note that there exist [functional](https://en.wikipedia.org/wiki/Functional_programming) programming languages, like [Scala](http://www.scala-lang.org/) or [Erlang](http://www.erlang.org/) that forbid changing variable values.
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 
 Em tais linguagens, uma vez que o valor é armazenado "na box", ele está lá para sempre. Se precisarmos de armazenar algo mais, a linguagem nos obriga a criar uma nova box (declarar uma nova variável). Não podemos reutilizar a antiga.
 
@@ -182,8 +187,13 @@ let my-name; // hífens '-' não são permitidos no nome
 Variáveis chamadas `apple` e `AppLE` são duas variáveis diferentes.
 ```
 
+<<<<<<< HEAD
 ````smart header="Letras não inglesas são permitidas, mas não são recomendadas"
 É possível usar qualquer idioma, incluindo letras cirílicas ou até hieróglifos, como este:
+=======
+````smart header="Non-Latin letters are allowed, but not recommended"
+It is possible to use any language, including cyrillic letters or even hieroglyphs, like this:
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 
 ```js
 let имя = '...';
@@ -254,7 +264,11 @@ Há uma prática generalizada de usar constantes como aliases para valores difí
 
 Tais constantes são nomeadas usando letras maiúsculas e sublinhados.
 
+<<<<<<< HEAD
 Como estas:
+=======
+For instance, let's make constants for colors in so-called "web" (hexadecimal) format:
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 
 ```js run
 const COLOR_RED = "#F00";
@@ -290,7 +304,11 @@ Em outras palavras, constantes com nomes maiúsculos são usadas apenas como pse
 
 Falando em variáveis, há mais uma coisa extremamente importante.
 
+<<<<<<< HEAD
 Por favor, nomeie as suas variáveis de forma sensata. Tome tempo para pensar sobre isso.
+=======
+A variable name should have a clean, obvious meaning, describe the data that it stores.
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 
 A nomenclatura variável é uma das habilidades mais importantes e complexas em programação. Uma rápida olhada em nomes de variáveis pode revelar qual código foi escrito por um iniciante versus um desenvolvedor experiente.
 
diff --git a/1-js/02-first-steps/05-types/article.md b/1-js/02-first-steps/05-types/article.md
index bb2d1fb15..e6a23e3b3 100644
--- a/1-js/02-first-steps/05-types/article.md
+++ b/1-js/02-first-steps/05-types/article.md
@@ -226,7 +226,11 @@ As três últimas linhas podem precisar de explicações adicionais:
 
 ## Resumo
 
+<<<<<<< HEAD
 Existem 7 tipos básicos em JavaScript.
+=======
+There are 7 basic data types in JavaScript.
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 
 - `number` para números de qualquer tipo: inteiro ou ponto flutuante.
 - `string` para cordas. Uma cadeia de caracteres pode ter um ou mais caracteres, não há nenhum tipo de caractere único separado.
diff --git a/1-js/02-first-steps/08-comparison/article.md b/1-js/02-first-steps/08-comparison/article.md
index 3d5cc1729..8697076a4 100644
--- a/1-js/02-first-steps/08-comparison/article.md
+++ b/1-js/02-first-steps/08-comparison/article.md
@@ -193,7 +193,7 @@ Why does it dislike zero so much? Always false!
 We get these results because:
 
 - Comparisons `(1)` and `(2)` return `false` because `undefined` gets converted to `NaN` and `NaN` is a special numeric value which returns `false` for all comparisons.
-- The equality check `(3)` returns `false` because `undefined` only equals `null` and no other value.
+- The equality check `(3)` returns `false` because `undefined` only equals `null`, `undefined`, and no other value.
 
 ### Evade problems
 
diff --git a/1-js/02-first-steps/09-alert-prompt-confirm/article.md b/1-js/02-first-steps/09-alert-prompt-confirm/article.md
index f69c2d233..c14e0c85a 100644
--- a/1-js/02-first-steps/09-alert-prompt-confirm/article.md
+++ b/1-js/02-first-steps/09-alert-prompt-confirm/article.md
@@ -1,6 +1,6 @@
 # Interaction: alert, prompt, confirm
 
-This part of the tutorial aims to cover JavaScript "as is", without environment-specific tweaks.
+In this part of the tutorial we cover JavaScript language "as is", without environment-specific tweaks.
 
 But we'll still be using the browser as our demo environment, so we should know at least a few of its user-interface functions. In this chapter, we'll get familiar with the browser functions `alert`, `prompt` and `confirm`.
 
diff --git a/1-js/02-first-steps/10-ifelse/article.md b/1-js/02-first-steps/10-ifelse/article.md
index 1e12fa7b5..49c1fc041 100644
--- a/1-js/02-first-steps/10-ifelse/article.md
+++ b/1-js/02-first-steps/10-ifelse/article.md
@@ -2,7 +2,7 @@
 
 Sometimes, we need to perform different actions based on different conditions.
 
-To do that, we use the `if` statement and the conditional (ternary) operator which we will be referring to as the “question mark” operator `?` for simplicity.
+To do that, we can use the `if` statement and the conditional operator `?`, that's also called a "question mark" operator.
 
 ## The "if" statement
 
@@ -103,7 +103,7 @@ In the code above, JavaScript first checks `year < 2015`. If that is falsy, it g
 
 There can be more `else if` blocks. The final `else` is optional.
 
-## Ternary operator '?'
+## Conditional operator '?'
 
 Sometimes, we need to assign a variable depending on a condition.
 
@@ -124,9 +124,9 @@ if (age > 18) {
 alert(accessAllowed);
 ```
 
-The so-called "ternary" or "question mark" operator lets us do that in a shorter and simpler way.
+The so-called "conditional" or "question mark" operator lets us do that in a shorter and simpler way.
 
-The operator is represented by a question mark `?`.  The formal term "ternary" means that the operator has three operands. It is actually the one and only operator in JavaScript which has that many.
+The operator is represented by a question mark `?`. Sometimes it's called "ternary", because the operator has three operands. It is actually the one and only operator in JavaScript which has that many.
 
 The syntax is:
 ```js
@@ -141,7 +141,7 @@ For example:
 let accessAllowed = (age > 18) ? true : false;
 ```
 
-Technically, we can omit the parentheses around `age > 18`. The question mark operator has a low precedence, so it executes after the comparison `>`. 
+Technically, we can omit the parentheses around `age > 18`. The question mark operator has a low precedence, so it executes after the comparison `>`.
 
 This example will do the same thing as the previous one:
 
diff --git a/1-js/02-first-steps/11-logical-operators/article.md b/1-js/02-first-steps/11-logical-operators/article.md
index 4932020ae..0773a10cb 100644
--- a/1-js/02-first-steps/11-logical-operators/article.md
+++ b/1-js/02-first-steps/11-logical-operators/article.md
@@ -84,7 +84,7 @@ The OR `||` operator does the following:
 
 A value is returned in its original form, without the conversion.
 
-In other words, a chain of OR `"||"` returns the first truthy value or the last one if no such value is found.
+In other words, a chain of OR `"||"` returns the first truthy value or the last one if no truthy value is found.
 
 For instance:
 
@@ -101,7 +101,7 @@ This leads to some interesting usage compared to a "pure, classical, boolean-onl
 
 1. **Getting the first truthy value from a list of variables or expressions.**
 
-    Imagine we have several variables which can either contain data or be `null/undefined`. How can we find the first one with data?
+    Imagine we have a list of variables which can either contain data or be `null/undefined`. How can we find the first one with data?
 
     We can use OR `||`:
 
@@ -143,7 +143,7 @@ This leads to some interesting usage compared to a "pure, classical, boolean-onl
     alert(x); // 1
     ```
 
-    An assignment is a simple case. Other side effects can also be involved.
+    An assignment is a simple case. There may be side effects, that won't show up if the evaluation doesn't reach them.
 
     As we can see, such a use case is a "shorter way of doing `if`". The first operand is converted to boolean. If it's false, the second one is evaluated.
 
diff --git a/1-js/02-first-steps/12-while-for/article.md b/1-js/02-first-steps/12-while-for/article.md
index 992c21af6..c809581f5 100644
--- a/1-js/02-first-steps/12-while-for/article.md
+++ b/1-js/02-first-steps/12-while-for/article.md
@@ -47,8 +47,8 @@ while (i) { // when i becomes 0, the condition becomes falsy, and the loop stops
 }
 ```
 
-````smart header="Brackets are not required for a single-line body"
-If the loop body has a single statement, we can omit the brackets `{…}`:
+````smart header="Curly braces are not required for a single-line body"
+If the loop body has a single statement, we can omit the curly braces `{…}`:
 
 ```js run
 let i = 3;
diff --git a/1-js/02-first-steps/14-function-basics/article.md b/1-js/02-first-steps/14-function-basics/article.md
index 18833cbf1..ec34b744d 100644
--- a/1-js/02-first-steps/14-function-basics/article.md
+++ b/1-js/02-first-steps/14-function-basics/article.md
@@ -101,7 +101,7 @@ showMessage();
 alert( userName ); // *!*Bob*/!*, the value was modified by the function
 ```
 
-The outer variable is only used if there's no local one. So an occasional modification may happen if we forget `let`.
+The outer variable is only used if there's no local one.
 
 If a same-named variable is declared inside the function then it *shadows* the outer one. For instance, in the code below the function uses the local `userName`. The outer one is ignored:
 
@@ -128,7 +128,7 @@ Variables declared outside of any function, such as the outer `userName` in the
 
 Global variables are visible from any function (unless shadowed by locals).
 
-Usually, a function declares all variables specific to its task. Global variables only store project-level data, and it's important that these variables are accessible from anywhere. Modern code has few or no globals. Most variables reside in their functions.
+It's a good practice to minimize the use of global variables. Modern code has few or no globals. Most variables reside in their functions. Sometimes though, they can be useful to store project-level data.
 ```
 
 ## Parameters
@@ -376,7 +376,7 @@ A few examples of breaking this rule:
 - `createForm` -- would be bad if it modifies the document, adding a form to it (should only create it and return).
 - `checkPermission` -- would be bad if it displays the `access granted/denied` message (should only perform the check and return the result).
 
-These examples assume common meanings of prefixes. What they mean for you is determined by you and your team. Maybe it's pretty normal for your code to behave differently. But you should have a firm understanding of what a prefix means, what a prefixed function can and cannot do. All same-prefixed functions should obey the rules. And the team should share the knowledge.
+These examples assume common meanings of prefixes. You and your team are free to agree on other meanings, but usually they're not much different. In any case, you should have a firm understanding of what a prefix means, what a prefixed function can and cannot do. All same-prefixed functions should obey the rules. And the team should share the knowledge.
 ```
 
 ```smart header="Ultrashort function names"
diff --git a/1-js/02-first-steps/15-function-expressions-arrows/article.md b/1-js/02-first-steps/15-function-expressions-arrows/article.md
index b4ea19bac..9b63907d5 100644
--- a/1-js/02-first-steps/15-function-expressions-arrows/article.md
+++ b/1-js/02-first-steps/15-function-expressions-arrows/article.md
@@ -175,7 +175,7 @@ We can pass it between variables and run when we want.
 
 Let's formulate the key differences between Function Declarations and Expressions.
 
-First, the syntax: how to see what is what in the code.
+First, the syntax: how to differentiate between them in the code.
 
 - *Function Declaration:* a function, declared as a separate statement, in the main code flow.
 
@@ -186,7 +186,7 @@ First, the syntax: how to see what is what in the code.
     }
     ```
 - *Function Expression:* a function, created inside an expression or inside another syntax construct. Here, the function is created at the right side of the "assignment expression" `=`:
-    
+
     ```js
     // Function Expression
     let sum = function(a, b) {
@@ -202,7 +202,7 @@ Once the execution flow passes to the right side of the assignment `let sum = fu
 
 Function Declarations are different.
 
-**A Function Declaration is usable in the whole script/code block.**
+**A Function Declaration is usable in the whole script (or a code block, if it's inside a block).**
 
 In other words, when JavaScript *prepares* to run the script or a code block, it first looks for Function Declarations in it and creates the functions. We can think of it as an "initialization stage".
 
diff --git a/1-js/02-first-steps/16-javascript-specials/article.md b/1-js/02-first-steps/16-javascript-specials/article.md
index e266861c7..b1aefd1d4 100644
--- a/1-js/02-first-steps/16-javascript-specials/article.md
+++ b/1-js/02-first-steps/16-javascript-specials/article.md
@@ -103,7 +103,7 @@ More in: <info:variables> and <info:types>.
 We're using a browser as a working environment, so basic UI functions will be:
 
 [`prompt(question, [default])`](mdn:api/Window/prompt)
-: Ask a `question`, and return either what the visitor entered or `null` if they pressed "cancel".
+: Ask a `question`, and return either what the visitor entered or `null` if they clicked "cancel".
 
 [`confirm(question)`](mdn:api/Window/confirm)
 : Ask a `question` and suggest to choose between Ok and Cancel. The choice is returned as `true/false`.
@@ -161,7 +161,7 @@ Comparisons
 
     Other comparisons convert to a number as well.
 
-    The strict equality operator `===` doesn't do the conversion: different types always mean different values for it, so:
+    The strict equality operator `===` doesn't do the conversion: different types always mean different values for it.
 
     Values `null` and `undefined` are special: they equal `==` each other and don't equal anything else.
 
diff --git a/1-js/03-code-quality/01-debugging-chrome/article.md b/1-js/03-code-quality/01-debugging-chrome/article.md
index eb9434864..2ca0d7003 100644
--- a/1-js/03-code-quality/01-debugging-chrome/article.md
+++ b/1-js/03-code-quality/01-debugging-chrome/article.md
@@ -20,7 +20,7 @@ Here's what you should see if you are doing it for the first time:
 
 The toggler button <span class="devtools" style="background-position:-168px -76px"></span> opens the tab with files.
 
-Let's click it and select `index.html` and then `hello.js` in the tree view. Here's what should show up:
+Let's click it and select `hello.js` in the tree view. Here's what should show up:
 
 ![](chrome-tabs.png)
 
@@ -34,7 +34,7 @@ Now you could click the same toggler <span class="devtools" style="background-po
 
 ## Console
 
-If we press `Esc`, then a console opens below. We can type commands there and press `key:Enter` to execute.
+If we press `key:Esc`, then a console opens below. We can type commands there and press `key:Enter` to execute.
 
 After a statement is executed, its result is shown below.
 
diff --git a/1-js/03-code-quality/06-polyfills/article.md b/1-js/03-code-quality/06-polyfills/article.md
index 907730fdc..f4df5998c 100644
--- a/1-js/03-code-quality/06-polyfills/article.md
+++ b/1-js/03-code-quality/06-polyfills/article.md
@@ -19,21 +19,20 @@ Here Babel comes to the rescue.
 
 Actually, there are two parts in Babel:
 
-1. First, the transpiler program, which rewrites the code. The developer runs it on their own computer. It rewrites the code into the older standard. And then the code is delivered to the website for users. Modern project build system like [webpack](http://webpack.github.io/) or [brunch](http://brunch.io/) provide means to run transpiler automatically on every code change, so that doesn't involve any time loss from our side.
+1. First, the transpiler program, which rewrites the code. The developer runs it on their own computer. It rewrites the code into the older standard. And then the code is delivered to the website for users. Modern project build system like [webpack](http://webpack.github.io/) provide means to run transpiler automatically on every code change, so that very easy to integrate into development process.
 
 2. Second, the polyfill.
 
-    The transpiler rewrites the code, so syntax features are covered. But for new functions we need to write a special script that implements them. JavaScript is a highly dynamic language, scripts may not just add new functions, but also modify built-in ones, so that they behave according to the modern standard.
+    New language features may include new built-in functions and syntax constructs.
+    The transpiler rewrites the code, transforming syntax constructs into older ones. But as for new built-in functions, we need to implement them. JavaScript is a highly dynamic language, scripts may add/modify any functions, so that they behave according to the modern standard.
 
-    There's a term "polyfill" for scripts that "fill in" the gap and add missing implementations.
+    A script that updates/adds new functions is called "polyfill". It "fills in" the gap and adds missing implementations.
 
     Two interesting polyfills are:
     - [babel polyfill](https://babeljs.io/docs/usage/polyfill/) that supports a lot, but is big.
     - [polyfill.io](http://polyfill.io) service that allows to load/construct polyfills on-demand, depending on the features we need.
 
-So, we need to setup the transpiler and add the polyfill for old engines to support modern features.
-
-If we orient towards modern engines and do not use features except those supported everywhere, then we don't need to use Babel.
+So, if we're going to use modern language features, a transpiler and a polyfill are necessary.
 
 ## Examples in the tutorial
 
@@ -49,9 +48,7 @@ Examples that use modern JS will work only if your browser supports it.
 ````
 
 ```offline
-As you're reading the offline version, examples are not runnable. But they usually work :)
+As you're reading the offline version, in PDF examples are not runnable. In EPUB some of them can run.
 ```
 
-[Chrome Canary](https://www.google.com/chrome/browser/canary.html) is good for all examples, but other modern browsers are mostly fine too.
-
-Note that on production we can use Babel to translate the code into suitable for less recent browsers, so there will be no such limitation, the code will run everywhere.
+Google Chrome is usually the most up-to-date with language features, good to run bleeding-edge demos without any transpilers, but other modern browsers also work fine.
diff --git a/1-js/04-object-basics/05-object-toprimitive/article.md b/1-js/04-object-basics/05-object-toprimitive/article.md
index a44cf4f4d..a7270aa66 100644
--- a/1-js/04-object-basics/05-object-toprimitive/article.md
+++ b/1-js/04-object-basics/05-object-toprimitive/article.md
@@ -3,28 +3,24 @@
 
 What happens when objects are added `obj1 + obj2`, subtracted `obj1 - obj2` or printed using `alert(obj)`?
 
-There are special methods in objects that do the conversion.
+In that case objects are auto-converted to primitives, and then the operation is carried out.
 
-In the chapter <info:type-conversions> we've seen the rules for numeric, string and boolean conversions of primitives. But we left a gap for objects. Now, as we know about methods and symbols it becomes possible to close it.
+In the chapter <info:type-conversions> we've seen the rules for numeric, string and boolean conversions of primitives. But we left a gap for objects. Now, as we know about methods and symbols it becomes possible to fill it.
 
-For objects, there's no to-boolean conversion, because all objects are `true` in a boolean context. So there are only string and numeric conversions.
-
-The numeric conversion happens when we subtract objects or apply mathematical functions. For instance, `Date` objects (to be covered in the chapter <info:date>) can be subtracted, and the result of `date1 - date2` is the time difference between two dates.
-
-As for the string conversion -- it usually happens when we output an object like `alert(obj)` and in similar contexts.
+1. All objects are `true` in a boolean context. There are only numeric and string conversions.
+2. The numeric conversion happens when we subtract objects or apply mathematical functions. For instance, `Date` objects (to be covered in the chapter <info:date>) can be subtracted, and the result of `date1 - date2` is the time difference between two dates.
+3. As for the string conversion -- it usually happens when we output an object like `alert(obj)` and in similar contexts.
 
 ## ToPrimitive
 
-When an object is used in the context where a primitive is required, for instance, in an `alert` or mathematical operations, it's converted to a primitive value using the `ToPrimitive` algorithm ([specification](https://tc39.github.io/ecma262/#sec-toprimitive)).
-
-That algorithm allows us to customize the conversion using a special object method.
+We can fine-tune string and numeric conversion, using special object methods.
 
-Depending on the context, the conversion has a so-called "hint".
+The conversion algorithm is called `ToPrimitive` in the [specification](https://tc39.github.io/ecma262/#sec-toprimitive). It's called with a "hint" that specifies the conversion type.
 
 There are three variants:
 
 `"string"`
-: When an operation expects a string, for object-to-string conversions, like `alert`:
+: For an object-to-string conversion, when we're doing an operation on an object that expects a string, like `alert`:
 
     ```js
     // output
@@ -35,7 +31,7 @@ There are three variants:
     ```
 
 `"number"`
-: When an operation expects a number, for object-to-number conversions, like maths:
+: For an object-to-number conversion, like when we're doing maths:
 
     ```js
     // explicit conversion
@@ -52,7 +48,7 @@ There are three variants:
 `"default"`
 : Occurs in rare cases when the operator is "not sure" what type to expect.
 
-    For instance, binary plus `+` can work both with strings (concatenates them) and numbers (adds them), so both strings and numbers would do. Or when an object is compared using `==` with a string, number or a symbol.
+    For instance, binary plus `+` can work both with strings (concatenates them) and numbers (adds them), so both strings and numbers would do. Or when an object is compared using `==` with a string, number or a symbol, it's also unclear which conversion should be done.
 
     ```js
     // binary plus
@@ -159,14 +155,21 @@ alert(user + 500); // toString -> John500
 
 In the absence of `Symbol.toPrimitive` and `valueOf`, `toString` will handle all primitive conversions.
 
-
-## ToPrimitive and ToString/ToNumber
+## Return types
 
 The important thing to know about all primitive-conversion methods is that they do not necessarily return the "hinted" primitive.
 
 There is no control whether `toString()` returns exactly a string, or whether `Symbol.toPrimitive` method returns a number for a hint "number".
 
-**The only mandatory thing: these methods must return a primitive.**
+The only mandatory thing: these methods must return a primitive, not an object.
+
+```smart header="Historical notes"
+For historical reasons, if `toString` or `valueOf` returns an object, there's no error, but such value is ignored (like if the method didn't exist). That's because in ancient times there was no good "error" concept in JavaScript.
+
+In contrast, `Symbol.toPrimitive` *must* return a primitive, otherwise there will be an error.
+```
+
+## Further operations
 
 An operation that initiated the conversion gets that primitive, and then continues to work with it, applying further conversions if necessary.
 
@@ -208,11 +211,6 @@ For instance:
     alert(obj + 2); // 3 (ToPrimitive returned boolean, not string => ToNumber)
     ```
 
-```smart header="Historical notes"
-For historical reasons, methods `toString` or `valueOf` *should* return a primitive: if any of them returns an object, then there's no error, but that object is ignored (like if the method didn't exist).
-
-In contrast, `Symbol.toPrimitive` *must* return a primitive, otherwise, there will be an error.
-```
 
 ## Summary
 
diff --git a/1-js/04-object-basics/06-constructor-new/article.md b/1-js/04-object-basics/06-constructor-new/article.md
index eb452f2f3..4a7922a70 100644
--- a/1-js/04-object-basics/06-constructor-new/article.md
+++ b/1-js/04-object-basics/06-constructor-new/article.md
@@ -83,7 +83,7 @@ let user = new function() {
 The constructor can't be called again, because it is not saved anywhere, just created and called. So this trick aims to encapsulate the code that constructs the single object, without future reuse.
 ````
 
-## Dual-syntax constructors: new.target
+## Constructor mode test: new.target
 
 ```smart header="Advanced stuff"
 The syntax from this section is rarely used, skip it unless you want to know everything.
@@ -109,7 +109,9 @@ new User(); // function User { ... }
 */!*
 ```
 
-That can be used to allow both `new` and regular calls to work the same. That is, create the same object:
+That can be used inside the function to know whether it was called with `new`, "in constructor mode", or without it, "in regular mode".
+
+We can also make both `new` and regular calls to do the same, like this:
 
 ```js run
 function User(name) {
diff --git a/1-js/05-data-types/01-primitives-methods/1-string-new-property/solution.md b/1-js/05-data-types/01-primitives-methods/1-string-new-property/solution.md
index 3205e40c2..92de3a39e 100644
--- a/1-js/05-data-types/01-primitives-methods/1-string-new-property/solution.md
+++ b/1-js/05-data-types/01-primitives-methods/1-string-new-property/solution.md
@@ -6,15 +6,22 @@ let str = "Olá";
 
 str.test = 5; // (*)
 
-alert(str.test); 
+alert(str.test);
 ```
 
+<<<<<<< HEAD
 Pode haver dois tipos de resultado:
 1. `undefined`
 2. Um erro.
+=======
+Depending on whether you have `use strict` or not, the result may be:
+1. `undefined` (no strict mode)
+2. An error (strict mode).
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 
 Por quê? Vamos examinar o que está acontecendo na linha`(*)`:
 
+<<<<<<< HEAD
 1. Quando a propriedade de `str` é acessada, um "invólucro de objeto" é criado.
 2. A operação com a propriedade é realizada nela. Então, o objeto obtém a propriedade `test`.
 3. A operação é concluída e o "invólucro de objeto" desaparece.
@@ -22,10 +29,21 @@ Por quê? Vamos examinar o que está acontecendo na linha`(*)`:
 Então, na última linha, `str` não tem nenhum traço da propriedade. Um novo invólucro de objeto para cada operação de objeto em uma string.
 
 Alguns navegadores podem decidir limitar ainda mais o programador e não permitir a atribuição de propriedades aos primitivos. É por isso que na prática também podemos ver erros na linha `(*)`. Porém é um pouco fora do escopo da especificação.
+=======
+1. When a property of `str` is accessed, a "wrapper object" is created.
+2. In strict mode, writing into it is an error.
+3. Otherwise, the operation with the property is carried on, the object gets the `test` property, but after that the "wrapper object" disappears.
+
+So, without strict mode, in the last line `str` has no trace of the property.
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 
 **Este exemplo mostra claramente que os primitivos não são objetos.**
 
+<<<<<<< HEAD
 Eles simplesmente não podem armazenar dados.
 
 Todas as operações de propriedade/método são executadas com a ajuda de objetos temporários.
 
+=======
+They can't store additional data.
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
diff --git a/1-js/05-data-types/01-primitives-methods/article.md b/1-js/05-data-types/01-primitives-methods/article.md
index 65372c478..d56cedb88 100644
--- a/1-js/05-data-types/01-primitives-methods/article.md
+++ b/1-js/05-data-types/01-primitives-methods/article.md
@@ -13,8 +13,13 @@ Um primitivo
 
 Um objeto
 
+<<<<<<< HEAD
 - É capaz de armazenar vários valores como propriedades.
 - Pode ser criado com `{}`, por exemplo: `{name: "John", age: 30}`. Existem outros tipos de objetos em JavaScript; funções, por exemplo, são objetos.
+=======
+- Is capable of storing multiple values as properties.
+- Can be created with `{}`, for instance: `{name: "John", age: 30}`. There are other kinds of objects in JavaScript: functions, for example, are objects.
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 
 Uma das melhores coisas sobre objetos é que podemos armazenar uma função como uma de suas propriedades.
 
@@ -46,9 +51,15 @@ Aqui está o paradoxo enfrentado pelo criador do JavaScript:
 
 A solução parece um pouco estranha, mas aqui está:
 
+<<<<<<< HEAD
 1. Primitivos ainda são primitivos. Um único valor, conforme desejado.
 2. A linguagem permite acesso a métodos e propriedades de strings, números, booleanos e símbolos.
 3. Quando isso acontece, um "invólucro de objeto" especial que fornece a funcionalidade extra é criado e, em seguida, é destruído.
+=======
+1. Primitives are still primitive. A single value, as desired.
+2. The language allows access to methods and properties of strings, numbers, booleans and symbols.
+3. In order for that to work, a special "object wrapper" that provides the extra functionality is created, and then is destroyed.
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 
 Os "invólucros de objeto" são diferentes para cada tipo primitivo e são chamados: `String`, `Number`, `Boolean` e `Symbol`. Assim, eles fornecem diferentes conjuntos de métodos.
 
@@ -91,18 +102,32 @@ Em JavaScript, isso também é possível por razões históricas, mas é altamen
 Por exemplo:
 
 ```js run
+<<<<<<< HEAD
 alert( typeof 1 ); // "número"
 
 alert( typeof new Number(1) ); // "objeto"!
 ```
 
 E por isso a seguir, `zero`, é um objeto, o alerta será mostrado:
+=======
+alert( typeof 0 ); // "number"
+
+alert( typeof new Number(0) ); // "object"!
+```
+
+Objects are always truthy in `if`, so here the alert will show up:
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 
 ```js run
 let zero = new Number(0);
 
+<<<<<<< HEAD
 if (zero) { // zero é true (verdadeiro), por que é um objeto
   alert( "zero é verdadeiro?!?" );
+=======
+if (zero) { // zero is true, because it's an object
+  alert( "zero is truthy!?!" );
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 }
 ```
 
diff --git a/1-js/05-data-types/02-number/article.md b/1-js/05-data-types/02-number/article.md
index 7ca012c27..a205f3e26 100644
--- a/1-js/05-data-types/02-number/article.md
+++ b/1-js/05-data-types/02-number/article.md
@@ -1,6 +1,6 @@
 # Numbers
 
-All numbers in JavaScript are stored in 64-bit format [IEEE-754](http://en.wikipedia.org/wiki/IEEE_754-1985), also known as "double precision".
+All numbers in JavaScript are stored in 64-bit format [IEEE-754](https://en.wikipedia.org/wiki/IEEE_754-2008_revision), also known as "double precision floating point numbers".
 
 Let's recap and expand upon what we currently know about them.
 
@@ -177,7 +177,7 @@ There are two ways to do so:
 
 ## Imprecise calculations
 
-Internally, a number is represented in 64-bit format [IEEE-754](http://en.wikipedia.org/wiki/IEEE_754-1985), so there are exactly 64 bits to store a number: 52 of them are used to store the digits, 11 of them store the position of the decimal point (they are zero for integer numbers), and 1 bit is for the sign.
+Internally, a number is represented in 64-bit format [IEEE-754](https://en.wikipedia.org/wiki/IEEE_754-2008_revision), so there are exactly 64 bits to store a number: 52 of them are used to store the digits, 11 of them store the position of the decimal point (they are zero for integer numbers), and 1 bit is for the sign.
 
 If a number is too big, it would overflow the 64-bit storage, potentially giving an infinity:
 
@@ -205,7 +205,7 @@ Ouch! There are more consequences than an incorrect comparison here. Imagine you
 
 But why does this happen?
 
-A number is stored in memory in its binary form, a sequence of ones and zeroes. But fractions like `0.1`, `0.2` that look simple in the decimal numeric system are actually unending fractions in their binary form.
+A number is stored in memory in its binary form, a sequence of bits - ones and zeroes. But fractions like `0.1`, `0.2` that look simple in the decimal numeric system are actually unending fractions in their binary form.
 
 In other words, what is `0.1`? It is one divided by ten `1/10`, one-tenth. In decimal numeral system such numbers are easily representable. Compare it to one-third: `1/3`. It becomes an endless fraction `0.33333(3)`.
 
@@ -326,7 +326,7 @@ Please note that an empty or a space-only string is treated as `0` in all numeri
 There is a special built-in method [Object.is](mdn:js/Object/is) that compares values like `===`, but is more reliable for two edge cases:
 
 1. It works with `NaN`: `Object.is(NaN, NaN) === true`, that's a good thing.
-2. Values `0` and `-0` are different: `Object.is(0, -0) === false`, it rarely matters, but these values technically are different.
+2. Values `0` and `-0` are different: `Object.is(0, -0) === false`, technically that's true, because internally the number has a sign bit that may be different even if all other bits are zeroes.
 
 In all other cases, `Object.is(a, b)` is the same as `a === b`.
 
diff --git a/1-js/05-data-types/03-string/1-ucfirst/solution.md b/1-js/05-data-types/03-string/1-ucfirst/solution.md
index 4809cf123..527d3978c 100644
--- a/1-js/05-data-types/03-string/1-ucfirst/solution.md
+++ b/1-js/05-data-types/03-string/1-ucfirst/solution.md
@@ -15,7 +15,7 @@ There are two variants here:
 
 Here's the 2nd variant:
 
-```js run
+```js run demo
 function ucFirst(str) {
   if (!str) return str;
 
diff --git a/1-js/05-data-types/03-string/2-check-spam/solution.md b/1-js/05-data-types/03-string/2-check-spam/solution.md
index 893c26497..de8dde57d 100644
--- a/1-js/05-data-types/03-string/2-check-spam/solution.md
+++ b/1-js/05-data-types/03-string/2-check-spam/solution.md
@@ -1,6 +1,6 @@
 To make the search case-insensitive, let's bring the string to lower case and then search:
 
-```js run
+```js run demo
 function checkSpam(str) {
   let lowerStr = str.toLowerCase();
 
diff --git a/1-js/05-data-types/03-string/2-check-spam/task.md b/1-js/05-data-types/03-string/2-check-spam/task.md
index d073adc05..3e7220951 100644
--- a/1-js/05-data-types/03-string/2-check-spam/task.md
+++ b/1-js/05-data-types/03-string/2-check-spam/task.md
@@ -4,7 +4,7 @@ importance: 5
 
 # Check for spam
 
-Write a function `checkSpam(str)` that returns `true` if `str` contains 'viagra' or 'XXX', otherwise `false.
+Write a function `checkSpam(str)` that returns `true` if `str` contains 'viagra' or 'XXX', otherwise false.
 
 The function must be case-insensitive:
 
diff --git a/1-js/05-data-types/04-array/article.md b/1-js/05-data-types/04-array/article.md
index 2fad1601d..2d6c225c9 100644
--- a/1-js/05-data-types/04-array/article.md
+++ b/1-js/05-data-types/04-array/article.md
@@ -1,12 +1,12 @@
-# Arrays 
+# Arrays
 
 Objects allow you to store keyed collections of values. That's fine.
 
-But quite often we find that we need an *ordered collection*, where we have a 1st, a 2nd, a 3rd element and so on. For example, we need that to store a list of something: users, goods, HTML elements etc. 
+But quite often we find that we need an *ordered collection*, where we have a 1st, a 2nd, a 3rd element and so on. For example, we need that to store a list of something: users, goods, HTML elements etc.
 
 It is not convenient to use an object here, because it provides no methods to manage the order of elements. We can’t insert a new property “between” the existing ones. Objects are just not meant for such use.
 
-There exists a special data structure named `Array`, to store ordered collections. 
+There exists a special data structure named `Array`, to store ordered collections.
 
 ## Declaration
 
@@ -81,10 +81,10 @@ arr[3](); // hello
 
 ````smart header="Trailing comma"
 An array, just like an object, may end with a comma:
-```js 
+```js
 let fruits = [
-  "Apple", 
-  "Orange", 
+  "Apple",
+  "Orange",
   "Plum"*!*,*/!*
 ];
 ```
@@ -95,7 +95,7 @@ The "trailing comma" style makes it easier to insert/remove items, because all l
 
 ## Methods pop/push, shift/unshift
 
-A [queue](https://en.wikipedia.org/wiki/Queue_(abstract_data_type)) is one of most common uses of an array. In computer science, this means an ordered collection of elements which supports two operations:
+A [queue](https://en.wikipedia.org/wiki/Queue_(abstract_data_type)) is one of the most common uses of an array. In computer science, this means an ordered collection of elements which supports two operations:
 
 - `push` appends an element to the end.
 - `shift` get an element from the beginning, advancing the queue, so that the 2nd element becomes the 1st.
@@ -106,7 +106,7 @@ Arrays support both operations.
 
 In practice we need it very often. For example, a queue of messages that need to be shown on-screen.
 
-There's another use case for arrays -- the data structure named [stack](https://en.wikipedia.org/wiki/Stack_(abstract_data_type)). 
+There's another use case for arrays -- the data structure named [stack](https://en.wikipedia.org/wiki/Stack_(abstract_data_type)).
 
 It supports two operations:
 
@@ -121,7 +121,7 @@ A stack is usually illustrated as a pack of cards: new cards are added to the to
 
 For stacks, the latest pushed item is received first, that's also called LIFO (Last-In-First-Out) principle. For queues, we have FIFO (First-In-First-Out).
 
-Arrays in JavaScript can work both as a queue and as a stack. They allow you to add/remove elements both to/from the beginning or the end. 
+Arrays in JavaScript can work both as a queue and as a stack. They allow you to add/remove elements both to/from the beginning or the end.
 
 In computer science the data structure that allows it is called [deque](https://en.wikipedia.org/wiki/Double-ended_queue).
 
@@ -189,11 +189,11 @@ alert( fruits );
 
 ## Internals
 
-An array is a special kind of object. The square brackets used to access a property `arr[0]` actually come from the object syntax. Numbers are used as keys. 
+An array is a special kind of object. The square brackets used to access a property `arr[0]` actually come from the object syntax. That's essentially the same as `obj[key]`, where `arr` is the object, while numbers are used as keys.
 
 They extend objects providing special methods to work with ordered collections of data and also the `length` property. But at the core it's still an object.
 
-Remember, there are only 7 basic types in JavaScript. Array is an object and thus behaves like an object. 
+Remember, there are only 7 basic types in JavaScript. Array is an object and thus behaves like an object.
 
 For instance, it is copied by reference:
 
@@ -203,7 +203,7 @@ let fruits = ["Banana"]
 let arr = fruits; // copy by reference (two variables reference the same array)
 
 alert( arr === fruits ); // true
- 
+
 arr.push("Pear"); // modify the array by reference
 
 alert( fruits ); // Banana, Pear - 2 items now
@@ -229,7 +229,7 @@ But the engine will see that we're working with the array as with a regular obje
 
 The ways to misuse an array:
 
-- Add a non-numeric property like `arr.test = 5`. 
+- Add a non-numeric property like `arr.test = 5`.
 - Make holes, like: add `arr[0]` and then `arr[1000]` (and nothing between them).
 - Fill the array in the reverse order, like `arr[1000]`, `arr[999]` and so on.
 
@@ -296,7 +296,7 @@ let fruits = ["Apple", "Orange", "Plum"];
 
 // iterates over array elements
 for (let fruit of fruits) {
-  alert( fruit ); 
+  alert( fruit );
 }
 ```
 
@@ -320,7 +320,7 @@ But that's actually a bad idea. There are potential problems with it:
 
     There are so-called "array-like" objects in the browser and in other environments, that *look like arrays*. That is, they have `length` and indexes properties, but they may also have other non-numeric properties and methods, which we usually don't need. The `for..in` loop will list them though. So if we need to work with array-like objects, then these "extra" properties can become a problem.
 
-2. The `for..in` loop is optimized for generic objects, not arrays, and thus is 10-100 times slower. Of course, it's still very fast. The speedup may only matter in bottlenecks or seem irrelevant. But still we should be aware of the difference.
+2. The `for..in` loop is optimized for generic objects, not arrays, and thus is 10-100 times slower. Of course, it's still very fast. The speedup may only matter in bottlenecks. But still we should be aware of the difference.
 
 Generally, we shouldn't use `for..in` for arrays.
 
@@ -338,7 +338,7 @@ fruits[123] = "Apple";
 alert( fruits.length ); // 124
 ```
 
-Note that we usually don't use arrays like that. 
+Note that we usually don't use arrays like that.
 
 Another interesting thing about the `length` property is that it's writable.
 
@@ -385,7 +385,7 @@ To evade such surprises, we usually use square brackets, unless we really know w
 
 ## Multidimensional arrays
 
-Arrays can have items that are also arrays. We can use it for multidimensional arrays, to store matrices:
+Arrays can have items that are also arrays. We can use it for multidimensional arrays, for example to store matrices:
 
 ```js run
 let matrix = [
@@ -445,7 +445,7 @@ Array is a special kind of object, suited to storing and managing ordered data i
 
     The call to `new Array(number)` creates an array with the given length, but without elements.
 
-- The `length` property is the array length or, to be precise, its last numeric index plus one. It is auto-adjusted by array methods. 
+- The `length` property is the array length or, to be precise, its last numeric index plus one. It is auto-adjusted by array methods.
 - If we shorten `length` manually, the array is truncated.
 
 We can use an array as a deque with the following operations:
@@ -461,4 +461,3 @@ To loop over the elements of the array:
   - `for (let i in arr)` -- never use.
 
 We will return to arrays and study more methods to add, remove, extract elements and sort arrays in the chapter <info:array-methods>.
-
diff --git a/1-js/05-data-types/05-array-methods/10-average-age/task.md b/1-js/05-data-types/05-array-methods/10-average-age/task.md
index a991c156b..bf5f85df3 100644
--- a/1-js/05-data-types/05-array-methods/10-average-age/task.md
+++ b/1-js/05-data-types/05-array-methods/10-average-age/task.md
@@ -4,7 +4,7 @@ importance: 4
 
 # Get average age
 
-Write the function `getAverageAge(users)` that gets an array of objects with property `age` and gets the average.
+Write the function `getAverageAge(users)` that gets an array of objects with property `age` and returns the average age.
 
 The formula for the average is `(age1 + age2 + ... + ageN) / N`.
 
@@ -19,4 +19,3 @@ let arr = [ john, pete, mary ];
 
 alert( getAverageAge(arr) ); // (25 + 30 + 29) / 3 = 28
 ```
-
diff --git a/1-js/05-data-types/05-array-methods/article.md b/1-js/05-data-types/05-array-methods/article.md
index 42bbd9465..1e2685580 100644
--- a/1-js/05-data-types/05-array-methods/article.md
+++ b/1-js/05-data-types/05-array-methods/article.md
@@ -36,7 +36,7 @@ That's natural, because `delete obj.key` removes a value by the `key`. It's all
 
 So, special methods should be used.
 
-The [arr.splice(str)](mdn:js/Array/splice) method is a swiss army knife for arrays. It can do everything: add, remove and insert elements.
+The [arr.splice(str)](mdn:js/Array/splice) method is a swiss army knife for arrays. It can do everything: insert, remove and replace elements.
 
 The syntax is:
 
@@ -239,7 +239,7 @@ These are methods to search for something in an array.
 The methods [arr.indexOf](mdn:js/Array/indexOf), [arr.lastIndexOf](mdn:js/Array/lastIndexOf) and [arr.includes](mdn:js/Array/includes) have the same syntax and do essentially the same as their string counterparts, but operate on items instead of characters:
 
 - `arr.indexOf(item, from)` looks for `item` starting from index `from`, and returns the index where it was found, otherwise `-1`.
-- `arr.lastIndexOf(item, from)` -- same, but looks from right to left.
+- `arr.lastIndexOf(item, from)` -- same, but looks for from right to left.
 - `arr.includes(item, from)` -- looks for `item` starting from index `from`, returns `true` if found.
 
 For instance:
diff --git a/1-js/05-data-types/06-iterable/article.md b/1-js/05-data-types/06-iterable/article.md
index 7f72f5caf..474d0463d 100644
--- a/1-js/05-data-types/06-iterable/article.md
+++ b/1-js/05-data-types/06-iterable/article.md
@@ -105,7 +105,7 @@ for (let num of range) {
 
 Now `range[Symbol.iterator]()` returns the `range` object itself:  it has the necessary `next()` method and remembers the current iteration progress in `this.current`. Shorter? Yes. And sometimes that's fine too.
 
-The downside is that now it's impossible to have two `for..of` loops running over the object simultaneously: they'll share the iteration state, because there's only one iterator -- the object itself. But two parallel for-ofs is a rare thing, doable with some async scenarios.
+The downside is that now it's impossible to have two `for..of` loops running over the object simultaneously: they'll share the iteration state, because there's only one iterator -- the object itself. But two parallel for-ofs is a rare thing, even in async scenarios.
 
 ```smart header="Infinite iterators"
 Infinite iterators are also possible. For instance, the `range` becomes infinite for `range.to = Infinity`. Or we can make an iterable object that generates an infinite sequence of pseudorandom numbers. Also can be useful.
@@ -144,7 +144,7 @@ Normally, internals of iterables are hidden from the external code. There's a `f
 
 But to understand things a little bit deeper let's see how to create an iterator explicitly.
 
-We'll iterate over a string the same way as `for..of`, but with direct calls. This code gets a string iterator and calls it "manually":
+We'll iterate over a string in exactlly the same way as `for..of`, but with direct calls. This code creates a string iterator and gets values from it "manually":
 
 ```js run
 let str = "Hello";
@@ -170,7 +170,9 @@ There are two official terms that look similar, but are very different. Please m
 - *Iterables* are objects that implement the `Symbol.iterator` method, as described above.
 - *Array-likes* are objects that have indexes and `length`, so they look like arrays.
 
-Naturally, these properties can combine. For instance, strings are both iterable (`for..of` works on them) and array-like (they have numeric indexes and `length`).
+When we use JavaScript for practical tasks in browser or other environments, we may meet objects that are iterables or array-likes, or both.
+
+For instance, strings are both iterable (`for..of` works on them) and array-like (they have numeric indexes and `length`).
 
 But an iterable may be not array-like. And vice versa an array-like may be not iterable.
 
@@ -191,11 +193,11 @@ for (let item of arrayLike) {}
 */!*
 ```
 
-What do they have in common? Both iterables and array-likes are usually *not arrays*, they don't have `push`, `pop` etc. That's rather inconvenient if we have such an object and want to work with it as with an array.
+Both iterables and array-likes are usually *not arrays*, they don't have `push`, `pop` etc. That's rather inconvenient if we have such an object and want to work with it as with an array. E.g. we would like to work with `range` using array methods. How to achieve that?
 
 ## Array.from
 
-There's a universal method [Array.from](mdn:js/Array/from) that brings them together. It takes an iterable or array-like value and makes a "real" `Array` from it. Then we can call array methods on it.
+There's a universal method [Array.from](mdn:js/Array/from) that takes an iterable or array-like value and makes a "real" `Array` from it. Then we can call array methods on it.
 
 For instance:
 
@@ -227,7 +229,7 @@ The full syntax for `Array.from` allows to provide an optional "mapping" functio
 Array.from(obj[, mapFn, thisArg])
 ```
 
-The second argument `mapFn` should be the function to apply to each element before adding to the array, and `thisArg` allows to set `this` for it.
+The optional second argument `mapFn` can be a function that will be applied to each element before adding to the array, and `thisArg` allows to set `this` for it.
 
 For instance:
 
diff --git a/1-js/06-advanced-functions/01-recursion/article.md b/1-js/06-advanced-functions/01-recursion/article.md
index 036ae7f51..735c75bf3 100644
--- a/1-js/06-advanced-functions/01-recursion/article.md
+++ b/1-js/06-advanced-functions/01-recursion/article.md
@@ -319,7 +319,7 @@ let company = {
 In other words, a company has departments.
 
 - A department may have an array of staff. For instance, `sales` department has 2 employees: John and Alice.
-- Or a department may split into subdepartments, like `development` has two branches: `sites` and `internals`. Each of them has the own staff.
+- Or a department may split into subdepartments, like `development` has two branches: `sites` and `internals`. Each of them has their own staff.
 - It is also possible that when a subdepartment grows, it divides into subsubdepartments (or teams).
 
     For instance, the `sites` department in the future may be split into teams for `siteA` and `siteB`. And they, potentially, can split even more. That's not on the picture, just something to have in mind.
diff --git a/1-js/06-advanced-functions/03-closure/article.md b/1-js/06-advanced-functions/03-closure/article.md
index 465ba3115..6f175a775 100644
--- a/1-js/06-advanced-functions/03-closure/article.md
+++ b/1-js/06-advanced-functions/03-closure/article.md
@@ -1,9 +1,9 @@
 
 # Closure
 
-JavaScript is a very function-oriented language. It gives us a lot of freedom. A function can be created at one moment, then copied to another variable or passed as an argument to another function and called from a totally different place later.
+JavaScript is a very function-oriented language. It gives us a lot of freedom. A function can be created dynamically,  copied to another variable or passed as an argument to another function and called from a totally different place later.
 
-We know that a function can access variables outside of it; this feature is used quite often.
+We know that a function can access variables outside of it, this feature is used quite often.
 
 But what happens when an outer variable changes? Does a function get the most recent value or the one that existed when the function was created?
 
@@ -63,24 +63,24 @@ Let's consider two situations to begin with, and then study the internal mechani
 
 To understand what's going on, let's first discuss what a "variable" actually is.
 
-In JavaScript, every running function, code block, and the script as a whole have an associated object known as the *Lexical Environment*.
+In JavaScript, every running function, code block `{...}`, and the script as a whole have an internal (hidden) associated object known as the *Lexical Environment*.
 
 The Lexical Environment object consists of two parts:
 
-1. *Environment Record* -- an object that has all local variables as its properties (and some other information like the value of `this`).
-2. A reference to the *outer lexical environment*, usually the one associated with the code lexically right outside of it (outside of the current curly brackets).
+1. *Environment Record* -- an object that stores all local variables as its properties (and some other information like the value of `this`).
+2. A reference to the *outer lexical environment*, the one associated with the outer code.
 
-**So, a "variable" is just a property of the special internal object, Environment Record. "To get or change a variable" means "to get or change a property of that object".**
+**So, a "variable" is just a property of the special internal object, `Environment Record`. "To get or change a variable" means "to get or change a property of that object".**
 
 For instance, in this simple code, there is only one Lexical Environment:
 
 ![lexical environment](lexical-environment-global.png)
 
-This is a so-called global Lexical Environment, associated with the whole script. For browsers, all `<script>` tags share the same global environment.
+This is a so-called global Lexical Environment, associated with the whole script.
 
 On the picture above, the rectangle means Environment Record (variable store) and the arrow means the outer reference. The global Lexical Environment has no outer reference, so it points to `null`.
 
-Here's the bigger picture of how `let` variables work:
+Here's the bigger picture of what happens when a `let` changes:
 
 ![lexical environment](lexical-environment-global-2.png)
 
@@ -89,7 +89,7 @@ Rectangles on the right-hand side demonstrate how the global Lexical Environment
 1. When the script starts, the Lexical Environment is empty.
 2. The `let phrase` definition appears. It has been assigned no value, so `undefined` is stored.
 3. `phrase` is assigned a value.
-4. `phrase` refers to a new value.
+4. `phrase` changes value.
 
 Everything looks simple for now, right?
 
@@ -140,14 +140,14 @@ So, during the function call we have two Lexical Environments: the inner one (fo
 
 - The inner Lexical Environment corresponds to the current execution of `say`.
 
-    It has a single variable: `name`, the function argument. We called `say("John")`, so the value of `name` is `"John"`.
+    It has a single property: `name`, the function argument. We called `say("John")`, so the value of `name` is `"John"`.
 - The outer Lexical Environment is the global Lexical Environment.
 
     It has `phrase` and the function itself.
 
 The inner Lexical Environment has a reference to the outer one.
 
-**When the code wants to access a variable -- the inner Lexical Environment is searched first, then the outer one, then the more outer one and so on until the end of the chain.**
+**When the code wants to access a variable -- the inner Lexical Environment is searched first, then the outer one, then the more outer one and so on until the global one.**
 
 If a variable is not found anywhere, that's an error in strict mode. Without `use strict`, an assignment to an undefined variable creates a new global variable, for backwards compatibility.
 
@@ -248,7 +248,7 @@ function makeCounter() {
   let count = 0;
 
   return function() {
-    return count++; // has access to the outer counter
+    return count++; // has access to the outer "count"
   };
 }
 
@@ -309,12 +309,10 @@ alert( counter2() ); // 0 (independent)
 ```
 
 
-Hopefully, the situation with outer variables is quite clear for you now. But in more complex situations a deeper understanding of internals may be required. So let's dive deeper.
+Hopefully, the situation with outer variables is clear now. For most situations such understanding is enough. There are few details in the specification that we omitted for brevity. So in the next section we cover even more details, not to miss anything.
 
 ## Environments in detail
 
-Now that you understand how closures work generally, that's already very good.
-
 Here's what's going on in the `makeCounter` example step-by-step, follow it to make sure that you know things in the very detail.
 
 Please note the additional `[[Environment]]` property is covered here. We didn't mention it before for simplicity.
@@ -351,7 +349,7 @@ Please note the additional `[[Environment]]` property is covered here. We didn't
 
     ![](lexenv-nested-makecounter-3.png)
 
-    Please note that on this step the inner function was created, but not yet called. The code inside `function() { return count++; }` is not running; we're going to return it soon.
+    Please note that on this step the inner function was created, but not yet called. The code inside `function() { return count++; }` is not running.
 
 4. As the execution goes on, the call to `makeCounter()` finishes, and the result (the tiny nested function) is assigned to the global variable `counter`:
 
@@ -451,7 +449,7 @@ Again, similarly to `if`, after the loop `i` is not visible.
 
 We also can use a "bare" code block `{…}` to isolate variables into a "local scope".
 
-For instance, in a web browser all scripts share the same global area. So if we create a global variable in one script, it becomes available to others. But that becomes a source of conflicts if two scripts use the same variable name and overwrite each other.
+For instance, in a web browser all scripts (except with `type="module"`) share the same global area. So if we create a global variable in one script, it becomes available to others. But that becomes a source of conflicts if two scripts use the same variable name and overwrite each other.
 
 That may happen if the variable name is a widespread word, and script authors are unaware of each other.
 
@@ -581,7 +579,7 @@ function f() {
   return function() { alert(value); };
 }
 
-// 3 functions in array, every one of them links to Lexical Environment
+// 3 functions in array, every one of them links to Lexical Environment (LE for short)
 // from the corresponding f() run
 //         LE   LE   LE
 let arr = [f(), f(), f()];
diff --git a/1-js/06-advanced-functions/06-function-object/article.md b/1-js/06-advanced-functions/06-function-object/article.md
index 37839779c..e907086c2 100644
--- a/1-js/06-advanced-functions/06-function-object/article.md
+++ b/1-js/06-advanced-functions/06-function-object/article.md
@@ -153,7 +153,7 @@ alert( `Called ${sayHi.counter} times` ); // Called 2 times
 ```warn header="A property is not a variable"
 A property assigned to a function like `sayHi.counter = 0` does *not* define a local variable `counter` inside it. In other words, a property `counter` and a variable `let counter` are two unrelated things.
 
-We can treat a function as an object, store properties in it, but that has no effect on its execution. Variables never use function properties and vice versa. These are just parallel worlds.
+We can treat a function as an object, store properties in it, but that has no effect on its execution. Variables are not function properties and vice versa. These are just parallel worlds.
 ```
 
 Function properties can replace closures sometimes. For instance, we can rewrite the counter function example from the chapter <info:closure> to use a function property:
@@ -340,7 +340,7 @@ Functions are objects.
 
 Here we covered their properties:
 
-- `name` -- the function name. Exists not only when given in the function definition, but also for assignments and object properties.
+- `name` -- the function name. Usually taken from the function definition, but if there's none, JavaScript tries to guess it from the context (e.g. an assignment).
 - `length` -- the number of arguments in the function definition. Rest parameters are not counted.
 
 If the function is declared as a Function Expression (not in the main code flow), and it carries the name, then it is called a Named Function Expression. The name can be used inside to reference itself, for recursive calls or such.
diff --git a/1-js/06-advanced-functions/08-settimeout-setinterval/1-output-numbers-100ms/solution.md b/1-js/06-advanced-functions/08-settimeout-setinterval/1-output-numbers-100ms/solution.md
index 13f01debf..f09372096 100644
--- a/1-js/06-advanced-functions/08-settimeout-setinterval/1-output-numbers-100ms/solution.md
+++ b/1-js/06-advanced-functions/08-settimeout-setinterval/1-output-numbers-100ms/solution.md
@@ -38,5 +38,27 @@ function printNumbers(from, to) {
 printNumbers(5, 10);
 ```
 
-Note that in both solutions, there is an initial delay before the first output. Sometimes we need to add a line to make the first output immediately, that's easy to do.
+Note that in both solutions, there is an initial delay before the first output. The function is called after `1000ms` the first time.
 
+If we also want the function to run immediately, then we can add an additional call on a separate line, like this:
+
+```js run
+function printNumbers(from, to) {
+  let current = from;
+
+  function go() {
+    alert(current);
+    if (current == to) {
+      clearInterval(timerId);
+    }
+    current++;
+  }
+
+*!*
+  go();
+*/!*
+  let timerId = setInterval(go, 1000);
+}
+
+printNumbers(5, 10);
+```
diff --git a/1-js/06-advanced-functions/08-settimeout-setinterval/article.md b/1-js/06-advanced-functions/08-settimeout-setinterval/article.md
index 91310f383..2ff7d6dcd 100644
--- a/1-js/06-advanced-functions/08-settimeout-setinterval/article.md
+++ b/1-js/06-advanced-functions/08-settimeout-setinterval/article.md
@@ -127,10 +127,10 @@ let timerId = setInterval(() => alert('tick'), 2000);
 setTimeout(() => { clearInterval(timerId); alert('stop'); }, 5000);
 ```
 
-```smart header="Modal windows freeze time in Chrome/Opera/Safari"
-In browsers IE and Firefox the internal timer continues "ticking" while showing `alert/confirm/prompt`, but in Chrome, Opera and Safari the internal timer becomes "frozen".
+```smart header="Time goes on while `alert` is shown"
+In most browsers, including Chrome and Firefox the internal timer continues "ticking" while showing `alert/confirm/prompt`.
 
-So if you run the code above and don't dismiss the `alert` window for some time, then in Firefox/IE next `alert` will be shown immediately as you do it (2 seconds passed from the previous invocation), and in Chrome/Opera/Safari -- after 2 more seconds (timer did not tick during the `alert`).
+So if you run the code above and don't dismiss the `alert` window for some time, then in the next `alert` will be shown immediately as you do it. The actual interval between alerts will be shorter than 5 seconds.
 ```
 
 ## Recursive setTimeout
@@ -176,7 +176,7 @@ let timerId = setTimeout(function request() {
 ```
 
 
-And if we regularly have CPU-hungry tasks, then we can measure the time taken by the execution and plan the next call sooner or later.
+And if we the functions that we're scheduling are CPU-hungry, then we can measure the time taken by the execution and plan the next call sooner or later.
 
 **Recursive `setTimeout` guarantees a delay between the executions, `setInterval` -- does not.**
 
@@ -354,7 +354,7 @@ function count() {
 count();
 ```
 
-Now when we start to `count()` and know that we'll need to `count()` more, we schedule that immediately, before doing the job.
+Now when we start to `count()` and see that we'll need to `count()` more, we schedule that immediately, before doing the job.
 
 If you run it, it's easy to notice that it takes significantly less time.
 
@@ -387,9 +387,9 @@ For server-side JavaScript, that limitation does not exist, and there exist othe
 
 ### Allowing the browser to render
 
-Another benefit for in-browser scripts is that they can show a progress bar or something to the user. That's because the browser usually does all "repainting" after the script is complete.
+Another benefit of splitting heavy tasks for browser scripts is that we can show a progress bar or something to the user.
 
-So if we do a single huge function then even if it changes something, the changes are not reflected in the document till it finishes.
+Usually the browser does all "repainting" after the currently running code is complete. So if we do a single huge function that changes many elements, the changes are not painted out till it finishes.
 
 Here's the demo:
 ```html run
@@ -402,7 +402,7 @@ Here's the demo:
     for (let j = 0; j < 1e6; j++) {
       i++;
       // put the current i into the <div>
-      // (we'll talk more about innerHTML in the specific chapter, should be obvious here)
+      // (we'll talk about innerHTML in the specific chapter, it just writes into element here)
       progress.innerHTML = i;
     }
   }
@@ -446,9 +446,9 @@ Now the `<div>` shows increasing values of `i`.
 - Methods `setInterval(func, delay, ...args)` and `setTimeout(func, delay, ...args)` allow to run the `func` regularly/once after `delay` milliseconds.
 - To cancel the execution, we should call `clearInterval/clearTimeout` with the value returned by `setInterval/setTimeout`.
 - Nested `setTimeout` calls is a more flexible alternative to `setInterval`. Also they can guarantee the minimal time *between* the executions.
-- Zero-timeout scheduling `setTimeout(...,0)` is used to schedule the call "as soon as possible, but after the current code is complete".
+- Zero-timeout scheduling `setTimeout(func, 0)` (the same as `setTimeout(func)`) is used to schedule the call "as soon as possible, but after the current code is complete".
 
-Some use cases of `setTimeout(...,0)`:
+Some use cases of `setTimeout(func)`:
 - To split CPU-hungry tasks into pieces, so that the script doesn't "hang"
 - To let the browser do something else while the process is going on (paint the progress bar).
 
diff --git a/1-js/06-advanced-functions/09-call-apply-decorators/04-throttle/task.md b/1-js/06-advanced-functions/09-call-apply-decorators/04-throttle/task.md
index 716b4e1d6..8dd77368d 100644
--- a/1-js/06-advanced-functions/09-call-apply-decorators/04-throttle/task.md
+++ b/1-js/06-advanced-functions/09-call-apply-decorators/04-throttle/task.md
@@ -12,13 +12,13 @@ Let's check the real-life application to better understand that requirement and
 
 **For instance, we want to track mouse movements.**
 
-In browser we can setup a function to run at every mouse micro-movement and get the pointer location as it moves. During an active mouse usage, this function usually runs very frequently, can be something like 100 times per second (every 10 ms).
+In browser we can setup a function to run at every mouse movement and get the pointer location as it moves. During an active mouse usage, this function usually runs very frequently, can be something like 100 times per second (every 10 ms).
 
 **The tracking function should update some information on the web-page.**
 
 Updating function `update()` is too heavy to do it on every micro-movement. There is also no sense in making it more often than once per 100ms.
 
-So we'll assign `throttle(update, 100)` as the function to run on each mouse move instead of the original `update()`. The decorator will be called often, but `update()` will be called at maximum once per 100ms.
+So we'll wrap it into the decorator: use `throttle(update, 100)` as the function to run on each mouse move instead of the original `update()`. The decorator will be called often, but `update()` will be called at maximum once per 100ms.
 
 Visually, it will look like this:
 
diff --git a/1-js/06-advanced-functions/09-call-apply-decorators/article.md b/1-js/06-advanced-functions/09-call-apply-decorators/article.md
index 75c510d1e..33a4bb8f3 100644
--- a/1-js/06-advanced-functions/09-call-apply-decorators/article.md
+++ b/1-js/06-advanced-functions/09-call-apply-decorators/article.md
@@ -453,7 +453,7 @@ let wrapper = function() {
 }
 ```
 
-We also saw an example of *method borrowing* when we take a method from an object and `call` it in the context of another object. It is quite common to take array methods and apply them to arguments. The alternative is to use rest parameters object that is a real array.
+We also saw an example of *method borrowing* when we take a method from an object and `call` it in the context of another object. It is quite common to take array methods and apply them to `arguments`. The alternative is to use rest parameters object that is a real array.
 
 
 There are many decorators there in the wild. Check how well you got them by solving the tasks of this chapter.
diff --git a/1-js/06-advanced-functions/10-bind/5-question-use-bind/solution.md b/1-js/06-advanced-functions/10-bind/5-question-use-bind/solution.md
index 0cb673b12..403107ca6 100644
--- a/1-js/06-advanced-functions/10-bind/5-question-use-bind/solution.md
+++ b/1-js/06-advanced-functions/10-bind/5-question-use-bind/solution.md
@@ -38,6 +38,6 @@ An alternative solution could be:
 askPassword(() => user.loginOk(), () => user.loginFail());
 ```
 
-Usually that also works, but may fail in more complex situations where `user` has a chance of being overwritten between the moments of asking and running `() => user.loginOk()`. 
-
+Usually that also works and looks good.
 
+It's a bit less reliable though in more complex situations where `user` variable might change *after* `askPassword` is called, but *before* the visitor answers and calls `() => user.loginOk()`. 
diff --git a/1-js/06-advanced-functions/10-bind/5-question-use-bind/task.md b/1-js/06-advanced-functions/10-bind/5-question-use-bind/task.md
index eb19e6644..fe6a9b4eb 100644
--- a/1-js/06-advanced-functions/10-bind/5-question-use-bind/task.md
+++ b/1-js/06-advanced-functions/10-bind/5-question-use-bind/task.md
@@ -2,7 +2,7 @@ importance: 5
 
 ---
 
-# Ask losing this
+# Fix a function that loses "this"
 
 The call to `askPassword()` in the code below should check the password and then call `user.loginOk/loginFail` depending on the answer.
 
@@ -34,5 +34,3 @@ let user = {
 askPassword(user.loginOk, user.loginFail);
 */!*
 ```
-
-
diff --git a/1-js/06-advanced-functions/10-bind/article.md b/1-js/06-advanced-functions/10-bind/article.md
index aed139c1c..06e2000ff 100644
--- a/1-js/06-advanced-functions/10-bind/article.md
+++ b/1-js/06-advanced-functions/10-bind/article.md
@@ -100,7 +100,7 @@ The basic syntax is:
 ```js
 // more complex syntax will be little later
 let boundFunc = func.bind(context);
-````
+```
 
 The result of `func.bind(context)` is a special function-like "exotic object", that is callable as function and transparently passes the call to `func` setting `this=context`.
 
diff --git a/1-js/07-object-properties/02-property-accessors/article.md b/1-js/07-object-properties/02-property-accessors/article.md
index 43cd5ae6d..5b58b584b 100644
--- a/1-js/07-object-properties/02-property-accessors/article.md
+++ b/1-js/07-object-properties/02-property-accessors/article.md
@@ -85,10 +85,10 @@ alert(user.surname); // Cooper
 Now we have a "virtual" property. It is readable and writable, but in fact does not exist.
 
 ```smart header="Accessor properties are only accessible with get/set"
-Once a property is defined with `get prop()` or `set prop()`, it's an accessor property, not a data properety any more.
+Once a property is defined with `get prop()` or `set prop()`, it's an accessor property, not a data property any more.
 
-- If there's a getter -- we can read `object.prop`, othrewise we can't.
-- If there's a setter -- we can set `object.prop=...`, othrewise we can't.
+- If there's a getter -- we can read `object.prop`, otherwise we can't.
+- If there's a setter -- we can set `object.prop=...`, otherwise we can't.
 
 And in either case we can't `delete` an accessor property.
 ```
diff --git a/1-js/08-prototypes/01-prototype-inheritance/article.md b/1-js/08-prototypes/01-prototype-inheritance/article.md
index 1641de236..c4dd1aacb 100644
--- a/1-js/08-prototypes/01-prototype-inheritance/article.md
+++ b/1-js/08-prototypes/01-prototype-inheritance/article.md
@@ -12,7 +12,7 @@ In JavaScript, objects have a special hidden property `[[Prototype]]` (as named
 
 ![prototype](object-prototype-empty.png)
 
-That `[[Prototype]]` has a "magical" meaning. When we want to read a property from `object`, and it's missing, JavaScript automatically takes it from the prototype. In programming, such thing is called "prototypal inheritance". Many cool language features and programming techniques are based on it.
+The prototype is a little bit "magical". When we want to read a property from `object`, and it's missing, JavaScript automatically takes it from the prototype. In programming, such thing is called "prototypal inheritance". Many cool language features and programming techniques are based on it.
 
 The property `[[Prototype]]` is internal and hidden, but there are many ways to set it.
 
@@ -251,10 +251,80 @@ If we had other objects like `bird`, `snake` etc inheriting from `animal`, they
 
 As a result, methods are shared, but the object state is not.
 
+## for..in loop
+
+The `for..in` loops over inherited properties too.
+
+For instance:
+
+```js run
+let animal = {
+  eats: true
+};
+
+let rabbit = {
+  jumps: true,
+  __proto__: animal
+};
+
+*!*
+// Object.keys only return own keys
+alert(Object.keys(rabbit)); // jumps
+*/!*
+
+*!*
+// for..in loops over both own and inherited keys
+for(let prop in rabbit) alert(prop); // jumps, then eats
+*/!*
+```
+
+If that's not what we want, and we'd like to exclude inherited properties, there's a built-in method [obj.hasOwnProperty(key)](mdn:js/Object/hasOwnProperty): it returns `true` if `obj` has its own (not inherited) property named `key`.
+
+So we can filter out inherited properties (or do something else with them):
+
+```js run
+let animal = {
+  eats: true
+};
+
+let rabbit = {
+  jumps: true,
+  __proto__: animal
+};
+
+for(let prop in rabbit) {
+  let isOwn = rabbit.hasOwnProperty(prop);
+
+  if (isOwn) {
+    alert(`Our: ${prop}`); // Our: jumps
+  } else {
+    alert(`Inherited: ${prop}`); // Inherited: eats
+  }
+}
+```
+
+Here we have the following inheritance chain: `rabbit` inherits from `animal`, that inherits from `Object.prototype` (because `animal` is a literal object `{...}`, so it's by default), and then `null` above it:
+
+![](rabbit-animal-object.png)
+
+Note, there's one funny thing. Where is the method `rabbit.hasOwnProperty` coming from? We did not define it. Looking at the chain we can see that the method is provided by `Object.prototype.hasOwnProperty`. In other words, it's inherited.
+
+...But why `hasOwnProperty` does not appear in `for..in` loop, like `eats` and `jumps`, if it lists all inherited properties.
+
+The answer is simple: it's not enumerable. Just like all other properties of `Object.prototype`, it has `enumerable:false` flag. That's why they are not listed.
+
+```smart header="All other iteration methods ignore inherited properties"
+All other key/value-getting methods, such as `Object.keys`, `Object.values` and so on ignore inherited properties.
+
+They only operate on the object itself. Properties from the prototype are taken into account.
+```
+
 ## Summary
 
 - In JavaScript, all objects have a hidden `[[Prototype]]` property that's either another object or `null`.
 - We can use `obj.__proto__` to access it (a historical getter/setter, there are other ways, to be covered soon).
 - The object referenced by `[[Prototype]]` is called a "prototype".
-- If we want to read a property of `obj` or call a method, and it doesn't exist, then JavaScript tries to find it in the prototype. Write/delete operations work directly on the object, they don't use the prototype (unless the property is actually a setter).
+- If we want to read a property of `obj` or call a method, and it doesn't exist, then JavaScript tries to find it in the prototype.
+- Write/delete operations for act directly on the object, they don't use the prototype (assuming it's a data property, not is a setter).
 - If we call `obj.method()`, and the `method` is taken from the prototype, `this` still references `obj`. So methods always work with the current object even if they are inherited.
+- The `for..in` loop iterates over both own and inherited properties. All other key/value-getting methods only operate on the object itself.
diff --git a/1-js/08-prototypes/05-getting-all-properties/rabbit-animal-object.png b/1-js/08-prototypes/01-prototype-inheritance/rabbit-animal-object.png
similarity index 100%
rename from 1-js/08-prototypes/05-getting-all-properties/rabbit-animal-object.png
rename to 1-js/08-prototypes/01-prototype-inheritance/rabbit-animal-object.png
diff --git a/1-js/08-prototypes/05-getting-all-properties/rabbit-animal-object@2x.png b/1-js/08-prototypes/01-prototype-inheritance/rabbit-animal-object@2x.png
similarity index 100%
rename from 1-js/08-prototypes/05-getting-all-properties/rabbit-animal-object@2x.png
rename to 1-js/08-prototypes/01-prototype-inheritance/rabbit-animal-object@2x.png
diff --git a/1-js/08-prototypes/04-prototype-methods/article.md b/1-js/08-prototypes/04-prototype-methods/article.md
index 5a9838d1c..a9c21faaf 100644
--- a/1-js/08-prototypes/04-prototype-methods/article.md
+++ b/1-js/08-prototypes/04-prototype-methods/article.md
@@ -72,11 +72,11 @@ That's for historical reasons.
 
 - The `"prototype"` property of a constructor function works since very ancient times.
 - Later in the year 2012: `Object.create` appeared in the standard. It allowed to create objects with the given prototype, but did not allow to get/set it. So browsers implemented non-standard `__proto__` accessor that allowed to get/set a prototype at any time.
-- Later in the year 2015: `Object.setPrototypeOf` and `Object.getPrototypeOf` were added to the standard. The `__proto__` was de-facto implemented everywhere, so it made its way to the Annex B of the standard, that is optional for non-browser environments.
+- Later in the year 2015: `Object.setPrototypeOf` and `Object.getPrototypeOf` were added to the standard, to perform the same functionality as `__proto__`. As `__proto__` was de-facto implemented everywhere, it was kind-of deprecated and made its way to the Annex B of the standard, that is optional for non-browser environments.
 
 As of now we have all these ways at our disposal.
 
-Why was `__proto__` replaced by the functions? That's an interesting question, requiring us to understand why `__proto__` is bad. Read on to get the answer.
+Why was `__proto__` replaced by the functions `getPrototypeOf/setPrototypeOf`? That's an interesting question, requiring us to understand why `__proto__` is bad. Read on to get the answer.
 
 ```warn header="Don't reset `[[Prototype]]` unless the speed doesn't matter"
 Technically, we can get/set `[[Prototype]]` at any time. But usually we only set it once at the object creation time, and then do not modify: `rabbit` inherits from `animal`, and that is not going to change.
@@ -107,7 +107,7 @@ That shouldn't surprise us. The `__proto__` property is special: it must be eith
 
 But we didn't *intend* to implement such behavior, right? We want to store key/value pairs, and the key named `"__proto__"` was not properly saved. So that's a bug!
 
-Here the consequences are not terrible. But in other cases the prototype may indeed be changed, so the execution may go wrong in totally unexpected ways.
+Here the consequences are not terrible. But in other cases, we may be assigning object values, then the prototype may indeed be changed. As the result, the execution will go wrong in totally unexpected ways.
 
 What's worst -- usually developers do not think about such possibility at all. That makes such bugs hard to notice and even turn them into vulnerabilities, especially when JavaScript is used on server-side.
 
@@ -191,10 +191,10 @@ let clone = Object.create(Object.getPrototypeOf(obj), Object.getOwnPropertyDescr
 
 
 - [Object.keys(obj)](mdn:js/Object/keys) / [Object.values(obj)](mdn:js/Object/values) / [Object.entries(obj)](mdn:js/Object/entries) -- returns an array of enumerable own string property names/values/key-value pairs.
-- [Object.getOwnPropertySymbols(obj)](mdn:js/Object/getOwnPropertySymbols) -- returns an array of all own symbolic property names.
-- [Object.getOwnPropertyNames(obj)](mdn:js/Object/getOwnPropertyNames) -- returns an array of all own string property names.
-- [Reflect.ownKeys(obj)](mdn:js/Reflect/ownKeys) -- returns an array of all own property names.
-- [obj.hasOwnProperty(key)](mdn:js/Object/hasOwnProperty): it returns `true` if `obj` has its own (not inherited) property named `key`.
+- [Object.getOwnPropertySymbols(obj)](mdn:js/Object/getOwnPropertySymbols) -- returns an array of all own symbolic keys.
+- [Object.getOwnPropertyNames(obj)](mdn:js/Object/getOwnPropertyNames) -- returns an array of all own string keys.
+- [Reflect.ownKeys(obj)](mdn:js/Reflect/ownKeys) -- returns an array of all own keys.
+- [obj.hasOwnProperty(key)](mdn:js/Object/hasOwnProperty): it returns `true` if `obj` has its own (not inherited) keytt named `key`.
 
 We also made it clear that `__proto__` is a getter/setter for `[[Prototype]]` and resides in `Object.prototype`, just as other methods.
 
diff --git a/1-js/08-prototypes/05-getting-all-properties/article.md b/1-js/08-prototypes/05-getting-all-properties/article.md
deleted file mode 100644
index 345181786..000000000
--- a/1-js/08-prototypes/05-getting-all-properties/article.md
+++ /dev/null
@@ -1,83 +0,0 @@
-
-# Getting all properties
-
-There are many ways to get keys/values from an object.
-
-Most of them operate on the object itself, excluding the prototype, let's recall them:
-
-- [Object.keys(obj)](mdn:js/Object/keys) / [Object.values(obj)](mdn:js/Object/values) / [Object.entries(obj)](mdn:js/Object/entries) -- returns an array of enumerable own string property names/values/key-value pairs. These methods only list *enumerable* properties, and those that have *strings as keys*.
-
-If we want symbolic properties:
-
-- [Object.getOwnPropertySymbols(obj)](mdn:js/Object/getOwnPropertySymbols) -- returns an array of all own symbolic property names.
-
-If we want non-enumerable properties:
-
-- [Object.getOwnPropertyNames(obj)](mdn:js/Object/getOwnPropertyNames) -- returns an array of all own string property names.
-
-If we want *all* properties:
-
-- [Reflect.ownKeys(obj)](mdn:js/Reflect/ownKeys) -- returns an array of all own property names.
-
-These methods are a bit different about which properties they return, but all of them operate on the object itself. Properties from the prototype are not listed.
-
-## for..in loop
-
-The `for..in` loop is different: it loops over inherited properties too.
-
-For instance:
-
-```js run
-let animal = {
-  eats: true
-};
-
-let rabbit = {
-  jumps: true,
-  __proto__: animal
-};
-
-*!*
-// only own keys
-alert(Object.keys(rabbit)); // jumps
-*/!*
-
-*!*
-// inherited keys too
-for(let prop in rabbit) alert(prop); // jumps, then eats
-*/!*
-```
-
-If that's not what we want, and we'd like to exclude inherited properties, there's a built-in method [obj.hasOwnProperty(key)](mdn:js/Object/hasOwnProperty): it returns `true` if `obj` has its own (not inherited) property named `key`.
-
-So we can filter out inherited properties (or do something else with them):
-
-```js run
-let animal = {
-  eats: true
-};
-
-let rabbit = {
-  jumps: true,
-  __proto__: animal
-};
-
-for(let prop in rabbit) {
-  let isOwn = rabbit.hasOwnProperty(prop);
-  alert(`${prop}: ${isOwn}`); // jumps: true, then eats: false
-}
-```
-
-Here we have the following inheritance chain: `rabbit`, then `animal`, then `Object.prototype` (because `animal` is a literal object `{...}`, so it's by default), and then `null` above it:
-
-![](rabbit-animal-object.png)
-
-Note, there's one funny thing. Where is the method `rabbit.hasOwnProperty` coming from? Looking at the chain we can see that the method is provided by `Object.prototype.hasOwnProperty`. In other words, it's inherited.
-
-...But why `hasOwnProperty` does not appear in `for..in` loop, if it lists all inherited properties?  The answer is simple: it's not enumerable. Just like all other properties of `Object.prototype`. That's why they are not listed.
-
-## Summary
-
-Most methods ignore inherited properties, with a notable exception of `for..in`.
-
-For the latter we can use [obj.hasOwnProperty(key)](mdn:js/Object/hasOwnProperty): it returns `true` if `obj` has its own (not inherited) property named `key`.
diff --git a/1-js/09-classes/01-class/article.md b/1-js/09-classes/01-class/article.md
index d78d00911..0c10960ca 100644
--- a/1-js/09-classes/01-class/article.md
+++ b/1-js/09-classes/01-class/article.md
@@ -168,12 +168,12 @@ Although, there are important differences.
     alert(User); // class User { ... }
     ```
 
-2. Class methods are non-enumerable
+2. Class methods are non-enumerable.
     A class definition sets `enumerable` flag to `false` for all methods in the `"prototype"`.
 
     That's good, because if we `for..in` over an object, we usually don't want its class methods.
 
-3. Classes always `use strict`
+3. Classes always `use strict`.
     All code inside the class construct is automatically in strict mode.
 
 
@@ -232,7 +232,7 @@ new User().sayHi(); // Hello
 
 ## Getters/setters, other shorthands
 
-Classes also include getters/setters, generators, computed properties etc.
+Just like literal objects, classes may include getters/setters, generators, computed properties etc.
 
 Here's an example for `user.name` implemented using `get/set`:
 
@@ -241,7 +241,7 @@ class User {
 
   constructor(name) {
     // invokes the setter
-    this._name = name;
+    this.name = name;
   }
 
 *!*
@@ -325,24 +325,6 @@ The property is not placed into `User.prototype`. Instead, it is created by `new
 
 ## Summary
 
-JavaScript provides many ways to create a class.
-
-First, as per the general object-oriented terminology, a class is something that provides "object templates", allows to create same-structured objects.
-
-When we say "a class", that doesn't necessary means the `class` keyword.
-
-This is a class:
-
-```js
-function User(name) {
-  this.sayHi = function() {
-    alert(name);
-  }
-}
-```
-
-...But in most cases `class` keyword is used, as it provides great syntax and many additional features.
-
 The basic class syntax looks like this:
 
 ```js
@@ -363,6 +345,6 @@ class MyClass {
 }
 ```
 
-`MyClass` is technically a function, while methods are written to `MyClass.prototype`.
+`MyClass` is technically a function (the one that we provide as `constructor`), while methods, getters and settors are written to `MyClass.prototype`.
 
 In the next chapters we'll learn more about classes, including inheritance and other features.
diff --git a/1-js/09-classes/02-class-inheritance/article.md b/1-js/09-classes/02-class-inheritance/article.md
index 7d00d9bd1..abb7d1e33 100644
--- a/1-js/09-classes/02-class-inheritance/article.md
+++ b/1-js/09-classes/02-class-inheritance/article.md
@@ -49,7 +49,7 @@ Right now they are fully independent.
 
 But we'd want `Rabbit` to extend `Animal`. In other words, rabbits should be based on animals, have access to methods of `Animal` and extend them with its own methods.
 
-To inherit from another class, we should specify `"extends"` and the parent class before the brackets `{..}`.
+To inherit from another class, we should specify `"extends"` and the parent class before the braces `{..}`.
 
 Here `Rabbit` inherits from `Animal`:
 
@@ -209,7 +209,7 @@ With constructors it gets a little bit tricky.
 
 Till now, `Rabbit` did not have its own `constructor`.
 
-According to the [specification](https://tc39.github.io/ecma262/#sec-runtime-semantics-classdefinitionevaluation), if a class extends another class and has no `constructor`, then the following `constructor` is generated:
+According to the [specification](https://tc39.github.io/ecma262/#sec-runtime-semantics-classdefinitionevaluation), if a class extends another class and has no `constructor`, then the following "empty" `constructor` is generated:
 
 ```js
 class Rabbit extends Animal {
@@ -309,15 +309,15 @@ alert(rabbit.earLength); // 10
 
 Let's get a little deeper under the hood of `super`. We'll see some interesting things by the way.
 
-First to say, from all that we've learned till now, it's impossible for `super` to work.
+First to say, from all that we've learned till now, it's impossible for `super` to work at all!
 
-Yeah, indeed, let's ask ourselves, how it could technically work? When an object method runs, it gets the current object as `this`. If we call `super.method()` then, how to retrieve the `method`? Naturally, we need to take the `method` from the prototype of the current object. How, technically, we (or a JavaScript engine) can do it?
+Yeah, indeed, let's ask ourselves, how it could technically work? When an object method runs, it gets the current object as `this`. If we call `super.method()` then, it needs to retrieve the `method` from the prototype of the current object.
 
-Maybe we can get the method from `[[Prototype]]` of `this`, as `this.__proto__.method`? Unfortunately, that doesn't work.
+The task may seem simple, but it isn't. The engine knows the current object `this`, so it could get the parent `method` as `this.__proto__.method`. Unfortunately, such a "naive" solution won't work.
 
-Let's try to do it. Without classes, using plain objects for the sake of simplicity.
+Let's demonstrate the problem. Without classes, using plain objects for the sake of simplicity.
 
-Here, `rabbit.eat()` should call `animal.eat()` method of the parent object:
+In the example below, `rabbit.__proto__ = animal`. Now let's try: in `rabbit.eat()` we'll call `animal.eat()`, using `this.__proto__`:
 
 ```js run
 let animal = {
@@ -414,18 +414,16 @@ The problem can't be solved by using `this` alone.
 
 To provide the solution, JavaScript adds one more special internal property for functions: `[[HomeObject]]`.
 
-**When a function is specified as a class or object method, its `[[HomeObject]]` property becomes that object.**
+When a function is specified as a class or object method, its `[[HomeObject]]` property becomes that object.
 
-This actually violates the idea of "unbound" functions, because methods remember their objects. And `[[HomeObject]]` can't be changed, so this bound is forever. So that's a very important change in the language.
+Then `super` uses it to resolve the parent prototype and its methods.
 
-But this change is safe. `[[HomeObject]]` is used only for calling parent methods in `super`, to resolve the prototype. So it doesn't break compatibility.
-
-Let's see how it works for `super` -- again, using plain objects:
+Let's see how it works, first with plain objects:
 
 ```js run
 let animal = {
   name: "Animal",
-  eat() {         // [[HomeObject]] == animal
+  eat() {         // animal.eat.[[HomeObject]] == animal
     alert(`${this.name} eats.`);
   }
 };
@@ -433,7 +431,7 @@ let animal = {
 let rabbit = {
   __proto__: animal,
   name: "Rabbit",
-  eat() {         // [[HomeObject]] == rabbit
+  eat() {         // rabbit.eat.[[HomeObject]] == rabbit
     super.eat();
   }
 };
@@ -441,19 +439,75 @@ let rabbit = {
 let longEar = {
   __proto__: rabbit,
   name: "Long Ear",
-  eat() {         // [[HomeObject]] == longEar
+  eat() {         // longEar.eat.[[HomeObject]] == longEar
     super.eat();
   }
 };
 
 *!*
+// works correctly
 longEar.eat();  // Long Ear eats.
 */!*
 ```
 
-Every method remembers its object in the internal `[[HomeObject]]` property. Then `super` uses it to resolve the parent prototype.
+It works as intended, due to `[[HomeObject]]` mechanics. A method, such as `longEar.eat`, knows its `[[HomeObject]]` and takes the parent method from its prototype. Without any use of `this`.
+
+### Methods are not "free"
+
+As we've known before, generally functions are "free", not bound to objects in JavaScript. So they can be copied between objects and called with another `this`.
+
+The very existance of `[[HomeObject]]` violates that principle, because methods remember their objects. `[[HomeObject]]` can't be changed, so this bond is forever.
+
+The only place in the language where `[[HomeObject]]` is used -- is `super`. So, if a method does not use `super`, then we can still consider it free and copy between objects. But with `super` things may go wrong.
+
+Here's the demo of a wrong `super` call:
+
+```js run
+let animal = {
+  sayHi() {
+    console.log(`I'm an animal`);
+  }
+};
+
+let rabbit = {
+  __proto__: animal,
+  sayHi() {
+    super.sayHi();
+  }
+};
 
-`[[HomeObject]]` is defined for methods defined both in classes and in plain objects. But for objects, methods must be specified exactly the given way: as `method()`, not as `"method: function()"`.
+let plant = {
+  sayHi() {
+    console.log("I'm a plant");
+  }
+};
+
+let tree = {
+  __proto__: plant,
+*!*
+  sayHi: rabbit.sayHi // (*)
+*/!*
+};
+
+*!*
+tree.sayHi();  // I'm an animal (?!?)
+*/!*
+```
+
+A call to `tree.sayHi()` shows "I'm an animal". Definitevely wrong.
+
+The reason is simple:
+- In the line `(*)`, the method `tree.sayHi` was copied from `rabbit`. Maybe we just wanted to avoid code duplication?
+- So its `[[HomeObject]]` is `rabbit`, as it was created in `rabbit`. There's no way to change `[[HomeObject]]`.
+- The code of `tree.sayHi()` has `super.sayHi()` inside. It goes up from `rabbit` and takes the method from `animal`.
+
+![](super-homeobject-wrong.png)
+
+### Methods, not function properties
+
+`[[HomeObject]]` is defined for methods both in classes and in plain objects. But for objects, methods must be specified exactly as `method()`, not as `"method: function()"`.
+
+The difference may be non-essential for us, but it's important for JavaScript.
 
 In the example below a non-method syntax is used for comparison. `[[HomeObject]]` property is not set and the inheritance doesn't work:
 
@@ -475,3 +529,18 @@ let rabbit = {
 rabbit.eat();  // Error calling super (because there's no [[HomeObject]])
 */!*
 ```
+
+## Summary
+
+1. To extend a class: `class Child extends Parent`:
+    - That means `Child.prototype.__proto__` will be `Parent.prototype`, so methods are inherited.
+2. When overriding a constructor:
+    - We must call parent constructor as `super()` in `Child` constructor before using `this`.
+3. When overriding another method:
+    - We can use `super.method()` in a `Child` method to call `Parent` method.
+4. Internals:
+    - Methods remember their class/object in the internal `[[HomeObject]]` property. That's how `super` resolves parent methods.
+    - So it's not safe to copy a method with `super` from one object to another.
+
+Also:
+- Arrow functions don't have own `this` or `super`, so they transparently fit into the surrounding context.
diff --git a/1-js/09-classes/02-class-inheritance/super-homeobject-wrong.png b/1-js/09-classes/02-class-inheritance/super-homeobject-wrong.png
new file mode 100644
index 000000000..b1871dc72
Binary files /dev/null and b/1-js/09-classes/02-class-inheritance/super-homeobject-wrong.png differ
diff --git a/1-js/09-classes/03-static-properties-methods/article.md b/1-js/09-classes/03-static-properties-methods/article.md
index 73a22a79f..b940e04c8 100644
--- a/1-js/09-classes/03-static-properties-methods/article.md
+++ b/1-js/09-classes/03-static-properties-methods/article.md
@@ -49,8 +49,8 @@ class Article {
 
 // usage
 let articles = [
-  new Article("Mind", new Date(2019, 1, 1)),
-  new Article("Body", new Date(2019, 0, 1)),
+  new Article("HTML", new Date(2019, 1, 1)),
+  new Article("CSS", new Date(2019, 0, 1)),
   new Article("JavaScript", new Date(2019, 11, 1))
 ];
 
@@ -58,7 +58,7 @@ let articles = [
 articles.sort(Article.compare);
 */!*
 
-alert( articles[0].title ); // Body
+alert( articles[0].title ); // CSS
 ```
 
 Here `Article.compare` stands "over" the articles, as a means to compare them. It's not a method of an article, but rather of the whole class.
@@ -171,7 +171,7 @@ rabbits[0].run(); // Black Rabbit runs with speed 5.
 
 Now we can call `Rabbit.compare` assuming that the inherited `Animal.compare` will be called.
 
-How does it work? Again, using prototypes. As you might have already guessed, extends also gives `Rabbit` the `[[Prototype]]` reference to `Animal`.
+How does it work? Again, using prototypes. As you might have already guessed, `extends` gives `Rabbit` the `[[Prototype]]` reference to `Animal`.
 
 
 ![](animal-rabbit-static.png)
@@ -187,10 +187,10 @@ class Rabbit extends Animal {}
 // for static properties and methods
 alert(Rabbit.__proto__ === Animal); // true
 
-// and the next step is Function.prototype
+// the next step up leads to Function.prototype
 alert(Animal.__proto__ === Function.prototype); // true
 
-// that's in addition to the "normal" prototype chain for object methods
+// the "normal" prototype chain for object methods
 alert(Rabbit.prototype.__proto__ === Animal.prototype);
 ```
 
diff --git a/1-js/09-classes/04-private-protected-properties-methods/article.md b/1-js/09-classes/04-private-protected-properties-methods/article.md
index 6cd9cc5fb..78d6c78f5 100644
--- a/1-js/09-classes/04-private-protected-properties-methods/article.md
+++ b/1-js/09-classes/04-private-protected-properties-methods/article.md
@@ -164,14 +164,14 @@ class CoffeeMachine {
   }
 
   *!*getWaterAmount()*/!* {
-    return this.waterAmount;
+    return this._waterAmount;
   }
 }
 
 new CoffeeMachine().setWaterAmount(100);
 ```
 
-That looks a bit longer, but functions are more flexible. They can accept multiple arguments (even if we don't need them right now). So, for the future, just in case we need to refactor something, functions are a safer choise.
+That looks a bit longer, but functions are more flexible. They can accept multiple arguments (even if we don't need them right now). So, for the future, just in case we need to refactor something, functions are a safer choice.
 
 Surely, there's a tradeoff. On the other hand, get/set syntax is shorter, so ultimately there's no strict rule, it's up to you to decide.
 ````
@@ -215,7 +215,7 @@ class CoffeeMachine {
   }
 
   get waterAmount() {
-    return this.waterAmount;
+    return this._waterAmount;
   }
 
 }
@@ -262,7 +262,7 @@ Unlike protected ones, private fields are enforced by the language itself. That'
 But if we inherit from `CoffeeMachine`, then we'll have no direct access to `#waterAmount`. We'll need to rely on `waterAmount` getter/setter:
 
 ```js
-class CoffeeMachine extends CoffeeMachine() {
+class MegaCoffeeMachine extends CoffeeMachine() {
   method() {
 *!*
     alert( this.#waterAmount ); // Error: can only access from CoffeeMachine
diff --git a/1-js/09-classes/05-extend-natives/article.md b/1-js/09-classes/05-extend-natives/article.md
index 63ea96cb5..f85aa0242 100644
--- a/1-js/09-classes/05-extend-natives/article.md
+++ b/1-js/09-classes/05-extend-natives/article.md
@@ -28,12 +28,11 @@ In the example above,
 arr.constructor === PowerArray
 ```
 
-So when `arr.filter()` is called, it internally creates the new array of results exactly as `new PowerArray`.
-That's actually very cool, because we can keep using `PowerArray` methods further on the result.
+So when `arr.filter()` is called, it internally creates the new array of results using exactly `new PowerArray`, not basic `Array`. That's actually very cool, because we can keep using `PowerArray` methods further on the result.
 
 Even more, we can customize that behavior.
 
-There's a special static getter `Symbol.species`, if exists, it returns the constructor to use in such cases.
+We can add a special static getter `Symbol.species` to the class. If exists, it should return the constructor that JavaScript will use internally to create new entities in `map`, `filter` and so on.
 
 If we'd like built-in methods like `map`, `filter` will return regular arrays, we can return `Array` in `Symbol.species`, like here:
 
@@ -69,11 +68,20 @@ As you can see, now `.filter` returns `Array`. So the extended functionality is
 
 Built-in objects have their own static methods, for instance `Object.keys`, `Array.isArray` etc.
 
-And we've already been talking about native classes extending each other: `Array.[[Prototype]] = Object`.
+As we already know, native classes extend each other. For instance, `Array` extends `Object`.
 
-But statics are an exception. Built-in classes don't inherit static properties from each other.
+Normally, when one class extends another, both static and non-static methods are inherited.
 
-In other words, the prototype of built-in constructor `Array` does not point to `Object`. This way `Array` and `Date` do not have `Array.keys` or `Date.keys`. And that feels natural.
+So, if `Rabbit extends Animal`, then:
+
+1. `Rabbit.methods` are callable for `Animal.methods`, because `Rabbit.[[Prototype]] = Animal`.
+2. `new Rabbit().methods` are also available, because `Rabbit.prototype.[[Prototype]] = Animal.prototype`.
+
+That's thoroughly explained in the chapter [](info:static-properties-methods#statics-and-inheritance).
+
+But built-in classes are an exception. They don't inherit statics `(1)` from each other.
+
+For example, both `Array` and `Date` inherit from `Object`, so their instances have methods from `Object.prototype`. But  `Array.[[Prototype]]` does not point to `Object`. So there's `Object.keys()`, but not `Array.keys()` and `Date.keys()`.
 
 Here's the picture structure for `Date` and `Object`:
 
diff --git a/1-js/09-classes/06-instanceof/article.md b/1-js/09-classes/06-instanceof/article.md
index 702c9e6b2..dca6ac627 100644
--- a/1-js/09-classes/06-instanceof/article.md
+++ b/1-js/09-classes/06-instanceof/article.md
@@ -46,14 +46,15 @@ alert( arr instanceof Object ); // true
 
 Please note that `arr` also belongs to the `Object` class. That's because `Array` prototypally inherits from `Object`.
 
-The `instanceof` operator examines the prototype chain for the check, and is also fine-tunable using the static method `Symbol.hasInstance`.
+The `instanceof` operator examines the prototype chain for the check, but we can set a custom logic the static method `Symbol.hasInstance`.
 
 The algorithm of `obj instanceof Class` works roughly as follows:
 
-1. If there's a static method `Symbol.hasInstance`, then use it. Like this:
+1. If there's a static method `Symbol.hasInstance`, then just call it: `Class[Symbol.hasInstance](obj)`. It should return either `true` or `false`. We're done.
+    For example: 
 
     ```js run
-    // assume anything that canEat is an animal
+    // setup instanceOf check that assumes that anything that canEat is an animal
     class Animal {
       static [Symbol.hasInstance](obj) {
         if (obj.canEat) return true;
@@ -61,10 +62,11 @@ The algorithm of `obj instanceof Class` works roughly as follows:
     }
 
     let obj = { canEat: true };
+
     alert(obj instanceof Animal); // true: Animal[Symbol.hasInstance](obj) is called
     ```
 
-2. Most classes do not have `Symbol.hasInstance`. In that case, check if `Class.prototype` equals to one of prototypes in the `obj` prototype chain.
+2. Most classes do not have `Symbol.hasInstance`. In that case, the standard logic is used: `obj instanceOf Classs` checks whether `Class.prototype` equals to one of prototypes in the `obj` prototype chain.
 
     In other words, compare:
     ```js
@@ -117,7 +119,7 @@ alert( rabbit instanceof Rabbit ); // false
 
 That's one of the reasons to avoid changing `prototype`. Just to keep safe.
 
-## Bonus: Object toString for the type
+## Bonus: Object.prototype.toString for the type
 
 We already know that plain objects are converted to string as `[object Object]`:
 
@@ -182,7 +184,7 @@ alert( {}.toString.call(user) ); // [object User]
 For most environment-specific objects, there is such a property. Here are few browser specific examples:
 
 ```js run
-// toStringTag for the envinronment-specific object and class:
+// toStringTag for the environment-specific object and class:
 alert( window[Symbol.toStringTag]); // window
 alert( XMLHttpRequest.prototype[Symbol.toStringTag] ); // XMLHttpRequest
 
diff --git a/1-js/10-error-handling/1-try-catch/1-finally-or-code-after/task.md b/1-js/10-error-handling/1-try-catch/1-finally-or-code-after/task.md
index e84687343..c573cc232 100644
--- a/1-js/10-error-handling/1-try-catch/1-finally-or-code-after/task.md
+++ b/1-js/10-error-handling/1-try-catch/1-finally-or-code-after/task.md
@@ -33,6 +33,6 @@ Compare the two code fragments.
     */!*
     ```
 
-We definitely need the cleanup after the work has started, doesn't matter if there was an error or not.
+We definitely need the cleanup after the work, doesn't matter if there was an error or not.
 
 Is there an advantage here in using `finally` or both code fragments are equal? If there is such an advantage, then give an example when it matters.
diff --git a/1-js/10-error-handling/1-try-catch/article.md b/1-js/10-error-handling/1-try-catch/article.md
index 797293582..4a1adba0c 100644
--- a/1-js/10-error-handling/1-try-catch/article.md
+++ b/1-js/10-error-handling/1-try-catch/article.md
@@ -68,7 +68,7 @@ Let's see more examples.
 
     } catch(err) {
 
-      alert(`Error has occured!`); // *!*(3) <--*/!*
+      alert(`Error has occurred!`); // *!*(3) <--*/!*
 
     }
 
@@ -108,7 +108,7 @@ try {
 }
 ```
 
-That's because `try..catch` actually wraps the `setTimeout` call that schedules the function. But the function itself is executed later, when the engine has already left the `try..catch` construct.
+That's because the function itself is executed later, when the engine has already left the `try..catch` construct.
 
 To catch an exception inside a scheduled function, `try..catch` must be inside that function:
 ```js run
@@ -338,7 +338,7 @@ Now `catch` became a single place for all error handling: both for `JSON.parse`
 
 ## Rethrowing
 
-In the example above we use `try..catch` to handle incorrect data. But is it possible that *another unexpected error* occurs within the `try {...}` block? Like a variable is undefined or something else, not just that "incorrect data" thing.
+In the example above we use `try..catch` to handle incorrect data. But is it possible that *another unexpected error* occurs within the `try {...}` block? Like a programming error (variable is not defined) or something else, not just that "incorrect data" thing.
 
 Like this:
 
@@ -355,7 +355,7 @@ try {
 }
 ```
 
-Of course, everything's possible! Programmers do make mistakes. Even in open-source utilities used by millions for decades -- suddenly a crazy bug may be discovered that leads to terrible hacks (like it happened with the `ssh` tool).
+Of course, everything's possible! Programmers do make mistakes. Even in open-source utilities used by millions for decades -- suddenly a bug may be discovered that leads to terrible hacks.
 
 In our case, `try..catch` is meant to catch "incorrect data" errors. But by its nature, `catch` gets *all* errors from `try`. Here it gets an unexpected error, but still shows the same `"JSON Error"` message. That's wrong and also makes the code more difficult to debug.
 
@@ -489,7 +489,7 @@ The code has two ways of execution:
 1. If you answer "Yes" to "Make an error?", then `try -> catch -> finally`.
 2. If you say "No", then `try -> finally`.
 
-The `finally` clause is often used when we start doing something before `try..catch` and want to finalize it in any case of outcome.
+The `finally` clause is often used when we start doing something and want to finalize it in any case of outcome.
 
 For instance, we want to measure the time that a Fibonacci numbers function `fib(n)` takes. Naturally, we can start measuring before it runs and finish afterwards. But what if there's an error during the function call? In particular, the implementation of `fib(n)` in the code below returns an error for negative or non-integer numbers.
 
@@ -521,14 +521,14 @@ try {
 }
 */!*
 
-alert(result || "error occured");
+alert(result || "error occurred");
 
 alert( `execution took ${diff}ms` );
 ```
 
 You can check by running the code with entering `35` into `prompt` -- it executes normally, `finally` after `try`. And then enter `-1` -- there will be an immediate error, an the execution will take `0ms`. Both measurements are done correctly.
 
-In other words, there may be two ways to exit a function: either a `return` or `throw`. The `finally` clause handles them both.
+In other words, the function may finish with `return` or `throw`, that doesn't matter. The `finally` clause executes in both cases.
 
 
 ```smart header="Variables are local inside `try..catch..finally`"
@@ -643,7 +643,7 @@ They work like this:
 
 ## Summary
 
-The `try..catch` construct allows to handle runtime errors. It literally allows to try running the code and catch errors that may occur in it.
+The `try..catch` construct allows to handle runtime errors. It literally allows to "try" running the code and "catch" errors that may occur in it.
 
 The syntax is:
 
@@ -666,7 +666,7 @@ Error objects have following properties:
 - `name` -- the string with error name (error constructor name).
 - `stack` (non-standard) -- the stack at the moment of error creation.
 
-If error is not needed, we can omit it by using `catch {` instead of `catch(err) {`.
+If an error object is not needed, we can omit it by using `catch {` instead of `catch(err) {`.
 
 We can also generate our own errors using the `throw` operator. Technically, the argument of `throw` can be anything, but usually it's an error object inheriting from the built-in `Error` class. More on extending errors in the next chapter.
 
diff --git a/1-js/11-async/02-promise-basics/article.md b/1-js/11-async/02-promise-basics/article.md
index c4bb84eb1..bec6851af 100644
--- a/1-js/11-async/02-promise-basics/article.md
+++ b/1-js/11-async/02-promise-basics/article.md
@@ -8,7 +8,7 @@ Everyone is happy, because the people don't crowd you any more, and fans, becaus
 
 This is a real-life analogy for things we often have in programming:
 
-1. A "producing code" that does something and takes time. For instance, the code loads a remote script. That's a "singer".
+1. A "producing code" that does something and takes time. For instance, the code loads data over a network. That's a "singer".
 2. A "consuming code" that wants the result of the "producing code" once it's ready. Many functions  may need that result. These are the "fans".
 3. A *promise* is a special JavaScript object that links the "producing code" and the "consuming code" together. In terms of our analogy: this is the "subscription list". The "producing code" takes whatever time it needs to produce the promised result, and the "promise" makes that result available to all of the subscribed code when it's ready.
 
@@ -27,7 +27,7 @@ The function passed to `new Promise` is called the *executor*. When the promise
 The resulting `promise` object has internal properties:
 
 - `state` — initially "pending", then changes to either "fulfilled" or "rejected",
-- `result` — an arbitrary value of your choosing, initially `undefined`.
+- `result` — an arbitrary value, initially `undefined`.
 
 When the executor finishes the job, it should call one of the functions that it gets as arguments:
 
@@ -56,7 +56,7 @@ let promise = new Promise(function(resolve, reject) {
 We can see two things by running the code above:
 
 1. The executor is called automatically and immediately (by the `new Promise`).
-2. The executor receives two arguments: `resolve` and `reject` — these functions are pre-defined by the JavaScript engine. So we don't need to create them. Instead, we should write the executor to call them when ready.
+2. The executor receives two arguments: `resolve` and `reject` — these functions are pre-defined by the JavaScript engine. So we don't need to create them. We only should call one of them when ready.
 
 After one second of "processing" the executor calls `resolve("done")` to produce the result:
 
@@ -77,7 +77,7 @@ let promise = new Promise(function(resolve, reject) {
 
 To summarize, the executor should do a job (something that takes time usually) and then call `resolve` or `reject` to change the state of the corresponding Promise object.
 
-The Promise that is either resolved or rejected is called "settled", as opposed to a "pending" Promise.
+The Promise that is either resolved or rejected is called "settled", as opposed to a initially "pending" Promise.
 
 ````smart header="There can be only a single result or an error"
 The executor should call only one `resolve` or one `reject`. The promise's state change is final.
@@ -112,9 +112,9 @@ let promise = new Promise(function(resolve, reject) {
 });
 ```
 
-For instance, this might happen when we start to do a job but then see that everything has already been completed.
+For instance, this might happen when we start to do a job but then see that everything has already been completed and  cached.
 
-That's fine. We immediately have a resolved Promise, nothing wrong with that.
+That's fine. We immediately have a resolved promise.
 ````
 
 ```smart header="The `state` and `result` are internal"
@@ -140,15 +140,15 @@ promise.then(
 
 The first argument of `.then` is a function that:
 
-1. runs when the Promise is resolved, and
+1. runs when the promise is resolved, and
 2. receives the result.
 
 The second argument of `.then` is a function that:
 
-1. runs when the Promise is rejected, and
+1. runs when the promise is rejected, and
 2. receives the error.
 
-For instance, here's a reaction to a successfuly resolved promise:
+For instance, here's a reaction to a successfully resolved promise:
 
 ```js run
 let promise = new Promise(function(resolve, reject) {
@@ -233,10 +233,10 @@ new Promise((resolve, reject) => {
   .then(result => show result, err => show error)
 ```
 
-It's not exactly an alias though. There are several important differences:
+It's not exactly an alias of `then(f,f)` though. There are several important differences:
 
 1. A `finally` handler has no arguments. In `finally` we don't know whether the promise is successful or not. That's all right, as our task is usually to perform "general" finalizing procedures.
-2. Finally passes through results and errors to the next handler.
+2. A `finally` handler passes through results and errors to the next handler.
 
     For instance, here the result is passed through `finally` to `then`:
     ```js run
@@ -257,11 +257,11 @@ It's not exactly an alias though. There are several important differences:
       .catch(err => alert(err));  // <-- .catch handles the error object
     ```  
 
-    That's very convenient, because finally is not meant to process promise results. So it passes them through.
+    That's very convenient, because `finally` is not meant to process a promise result. So it passes it through.
 
     We'll talk more about promise chaining and result-passing between handlers in the next chapter.
 
-3. Last, but not least, `.finally(f)` is a more convenient syntax than `.then(f, f)`: no need to duplicate the function.
+3. Last, but not least, `.finally(f)` is a more convenient syntax than `.then(f, f)`: no need to duplicate the function `f`.
 
 ````smart header="On settled promises handlers runs immediately"
 If a promise is pending, `.then/catch/finally` handlers wait for the result. Otherwise, if a promise has already settled, they execute immediately:
@@ -290,7 +290,7 @@ function loadScript(src, callback) {
   script.src = src;
 
   script.onload = () => callback(null, script);
-  script.onerror = () => callback(new Error(`Script load error ` + src));
+  script.onerror = () => callback(new Error(`Script load error for ${src}`));
 
   document.head.append(script);
 }
@@ -307,7 +307,7 @@ function loadScript(src) {
     script.src = src;
 
     script.onload = () => resolve(script);
-    script.onerror = () => reject(new Error("Script load error: " + src));
+    script.onerror = () => reject(new Error(`Script load error for ${src}`));
 
     document.head.append(script);
   });
diff --git a/1-js/11-async/03-promise-chaining/article.md b/1-js/11-async/03-promise-chaining/article.md
index 62e05bdd6..b2ba231ec 100644
--- a/1-js/11-async/03-promise-chaining/article.md
+++ b/1-js/11-async/03-promise-chaining/article.md
@@ -283,14 +283,14 @@ fetch('/article/promise-chaining/user.json')
 
 Now let's do something with the loaded user.
 
-For instance, we can make one more request to github, load the user profile and show the avatar:
+For instance, we can make one more request to GitHub, load the user profile and show the avatar:
 
 ```js run
 // Make a request for user.json
 fetch('/article/promise-chaining/user.json')
   // Load it as json
   .then(response => response.json())
-  // Make a request to github
+  // Make a request to GitHub
   .then(user => fetch(`https://api.github.com/users/${user.name}`))
   // Load the response as json
   .then(response => response.json())
diff --git a/1-js/11-async/03-promise-chaining/head.html b/1-js/11-async/03-promise-chaining/head.html
index 31c6b4271..0a0075fb9 100644
--- a/1-js/11-async/03-promise-chaining/head.html
+++ b/1-js/11-async/03-promise-chaining/head.html
@@ -10,25 +10,6 @@
     document.head.append(script);
   });
 }
-
-class HttpError extends Error {
-  constructor(response) {
-    super(`${response.status} for ${response.url}`);
-    this.name = 'HttpError';
-    this.response = response;
-  }
-}
-
-function loadJson(url) {
-  return fetch(url)
-    .then(response => {
-      if (response.status == 200) {
-        return response.json();
-      } else {
-        throw new HttpError(response);
-      }
-    })
-}
 </script>
 
 <style>
diff --git a/1-js/11-async/04-promise-error-handling/article.md b/1-js/11-async/04-promise-error-handling/article.md
index ca67202aa..3424d099e 100644
--- a/1-js/11-async/04-promise-error-handling/article.md
+++ b/1-js/11-async/04-promise-error-handling/article.md
@@ -5,7 +5,7 @@ Asynchronous actions may sometimes fail: in case of an error the corresponding p
 
 Promise chaining is great at that aspect. When a promise rejects, the control jumps to the closest rejection handler down the chain. That's very convenient in practice.
 
-For instance, in the code below the URL is wrong (no such server) and `.catch` handles the error:
+For instance, in the code below the URL is wrong (no such site) and `.catch` handles the error:
 
 ```js run
 *!*
@@ -15,10 +15,10 @@ fetch('https://no-such-server.blabla') // rejects
   .catch(err => alert(err)) // TypeError: failed to fetch (the text may vary)
 ```
 
-Or, maybe, everything is all right with the server, but the response is not valid JSON:
+Or, maybe, everything is all right with the site, but the response is not valid JSON:
 
 ```js run
-fetch('/') // fetch works fine now, the server responds successfully
+fetch('/') // fetch works fine now, the server responds with the HTML page
 *!*
   .then(response => response.json()) // rejects: the page is HTML, not a valid json
 */!*
@@ -52,7 +52,7 @@ Normally, `.catch` doesn't trigger at all, because there are no errors. But if a
 
 ## Implicit try..catch
 
-The code of a promise executor and promise handlers has an "invisible `try..catch`" around it. If an error happens, it gets caught and treated as a rejection.
+The code of a promise executor and promise handlers has an "invisible `try..catch`" around it. If an exception happens, it gets caught and treated as a rejection.
 
 For instance, this code:
 
@@ -120,7 +120,7 @@ new Promise((resolve, reject) => {
 
   throw new Error("Whoops!");
 
-}).catch(function(error) { 
+}).catch(function(error) {
 
   alert("The error is handled, continue normally");
 
@@ -169,7 +169,7 @@ Let's improve error handling for the user-loading example.
 
 The promise returned by [fetch](mdn:api/WindowOrWorkerGlobalScope/fetch) rejects when it's impossible to make a request. For instance, a remote server is not available, or the URL is malformed. But if the remote server responds with error 404, or even error 500, then it's considered a valid response.
 
-What if the server returns a non-JSON page with error 500 in the line `(*)`? What if there's no such user, and github returns a page with error 404 at `(**)`?
+What if the server returns a non-JSON page with error 500 in the line `(*)`? What if there's no such user, and GitHub returns a page with error 404 at `(**)`?
 
 ```js run
 fetch('no-such-user.json') // (*)
@@ -211,15 +211,15 @@ loadJson('no-such-user.json') // (3)
   .catch(alert); // HttpError: 404 for .../no-such-user.json
 ```
 
-1. We make a custom class for HTTP Errors to distinguish them from other types of errors. Besides, the new class has a constructor that accepts `response` object and saves it in the error. So error-handling code will be able to access it.
+1. We make a custom class for HTTP Errors to distinguish them from other types of errors. Besides, the new class has a constructor that accepts `response` object and saves it in the error. So error-handling code will be able to access the response.
 2. Then we put together the requesting and error-handling code into a function that fetches the `url` *and* treats any non-200 status as an error. That's convenient, because we often need such logic.
 3. Now `alert` shows a more helpful descriptive message.
 
-The great thing about having our own class for errors is that we can easily check for it in error-handling code.
+The great thing about having our own class for errors is that we can easily check for it in error-handling code using `instanceof`.
 
 For instance, we can make a request, and then if we get 404 -- ask the user to modify the information.
 
-The code below loads a user with the given name from github. If there's no such user, then it asks for the correct name:
+The code below loads a user with the given name from GitHub. If there's no such user, then it asks for the correct name:
 
 ```js run
 function demoGithubUser() {
@@ -260,15 +260,17 @@ new Promise(function() {
   noSuchFunction(); // Error here (no such function)
 })
   .then(() => {
-    // zero or many promise handlers
+    // successful promise handlers, one or more
   }); // without .catch at the end!
 ```
 
-In case of an error, the promise state becomes "rejected", and the execution should jump to the closest rejection handler. But there is no such handler in the examples above. So the error gets "stuck".
+In case of an error, the promise state becomes "rejected", and the execution should jump to the closest rejection handler. But there is no such handler in the examples above. So the error gets "stuck". There's no code to handle it.
 
-In practice, just like with a regular unhandled errors, it means that something has terribly gone wrong, the script probably died.
+In practice, just like with a regular unhandled errors, it means that something has terribly gone wrong.
 
-Most JavaScript engines track such situations and generate a global error in that case. We can see it in the console.
+What happens when a regular error occurs and is not caught by `try..catch`? The script dies. Similar thing happens with unhandled promise rejections.
+
+The JavaScript engine tracks such rejections and generates a global error in that case. You can see it in the console if you run the example above.
 
 In the browser we can catch such errors using the event `unhandledrejection`:
 
@@ -299,7 +301,7 @@ In non-browser environments like Node.js there are other similar ways to track u
 
 - `.catch` handles promise rejections of all kinds: be it a `reject()` call, or an error thrown in a handler.
 - We should place `.catch` exactly in places where we want to handle errors and know how to handle them. The handler should analyze errors (custom error classes help) and rethrow unknown ones.
-- It's normal not to use `.catch` if we don't know how to handle errors (all errors are unrecoverable).
+- It's ok not to use `.catch` at all, if there's no way to recover from an error.
 - In any case we should have the `unhandledrejection` event handler (for browsers, and analogs for other environments), to track unhandled errors and inform the user (and probably our server) about the them, so that our app never "just dies".
 
 And finally, if we have load-indication, then `.finally` is a great handler to stop it when the fetch is complete:
@@ -316,7 +318,7 @@ function demoGithubUser() {
 *!*
     .finally(() => { // (2) stop the indication
       document.body.style.opacity = '';
-      return new Promise(resolve => setTimeout(resolve, 0)); // (*)
+      return new Promise(resolve => setTimeout(resolve)); // (*)
     })
 */!*
     .then(user => {
diff --git a/1-js/11-async/04-promise-error-handling/head.html b/1-js/11-async/04-promise-error-handling/head.html
index 31c6b4271..a0b741962 100644
--- a/1-js/11-async/04-promise-error-handling/head.html
+++ b/1-js/11-async/04-promise-error-handling/head.html
@@ -1,16 +1,4 @@
 <script>
-function loadScript(src) {
-  return new Promise(function(resolve, reject) {
-    let script = document.createElement('script');
-    script.src = src;
-
-    script.onload = () => resolve(script);
-    script.onerror = () => reject(new Error("Script load error: " + src));
-
-    document.head.append(script);
-  });
-}
-
 class HttpError extends Error {
   constructor(response) {
     super(`${response.status} for ${response.url}`);
diff --git a/1-js/11-async/05-promise-api/01-promise-errors-as-results/solution.md b/1-js/11-async/05-promise-api/01-promise-errors-as-results/solution.md
index 17ac6ba5d..e50a5d49c 100644
--- a/1-js/11-async/05-promise-api/01-promise-errors-as-results/solution.md
+++ b/1-js/11-async/05-promise-api/01-promise-errors-as-results/solution.md
@@ -12,7 +12,7 @@ Promise.all(
 
 Here we have an array of `fetch(...)` promises that goes to `Promise.all`.
 
-We can't change the way `Promise.all` works: if it detects an error, then it rejects with it. So we need to prevent any error from occurring. Instead, if a `fetch` error happens, we need to treat it as a "normal" result.
+We can't change the way `Promise.all` works: if any promise rejects with an error, then `Promise.all` as a whole rejects with it. So we need to prevent any error from occurring. Instead, if a `fetch` error happens, we need to treat it as a "normal" result.
 
 Here's how:
 
diff --git a/1-js/11-async/06-promisify/article.md b/1-js/11-async/06-promisify/article.md
index e72329ce1..7c84912b5 100644
--- a/1-js/11-async/06-promisify/article.md
+++ b/1-js/11-async/06-promisify/article.md
@@ -2,7 +2,7 @@
 
 Promisification -- is a long word for a simple transform. It's conversion of a function that accepts a callback into a function returning a promise.
 
-In other words, we create a wrapper-function that does the same, internally calling the original one, but returns a promise.
+To be more precise, we create a wrapper-function that does the same, internally calling the original one, but returns a promise.
 
 Such transforms are often needed in real-life, as many functions and libraries are callback-based. But promises are more convenient. So it makes sense to promisify those.
 
@@ -105,7 +105,7 @@ f = promisify(f, true);
 f(...).then(arrayOfResults => ..., err => ...)
 ```
 
-In some cases, `err` may be absent at all: `callback(result)`, or there's something exotic in the callback format, then we can promisify such functions manually.
+In some cases, `err` may be absent at all: `callback(result)`, or there's something exotic in the callback format, then we can promisify such functions without using the helper, manually.
 
 There are also modules with a bit more flexible promisification functions, e.g. [es6-promisify](https://github.com/digitaldesignlabs/es6-promisify). In Node.js, there's a built-in `util.promisify` function for that.
 
diff --git a/1-js/11-async/07-microtask-queue/article.md b/1-js/11-async/07-microtask-queue/article.md
index 993042e57..29179c19f 100644
--- a/1-js/11-async/07-microtask-queue/article.md
+++ b/1-js/11-async/07-microtask-queue/article.md
@@ -167,7 +167,7 @@ setTimeout(() => promise.catch(err => alert('caught')));
 window.addEventListener('unhandledrejection', event => alert(event.reason));
 ```
 
-Now the unhandled rejction appears again. Why? Because `unhandledrejection` triggers when the microtask queue is complete. The engine examines promises and, if any of them is in "rejected" state, then the event is generated.
+Now the unhandled rejection appears again. Why? Because `unhandledrejection` triggers when the microtask queue is complete. The engine examines promises and, if any of them is in "rejected" state, then the event is generated.
 
 In the example, the `.catch` added by `setTimeout` triggers too, of course it does, but later, after `unhandledrejection` has already occurred.
 
diff --git a/1-js/11-async/08-async-await/01-rewrite-async/solution.md b/1-js/11-async/08-async-await/01-rewrite-async/solution.md
index c736defe9..6d9b339f6 100644
--- a/1-js/11-async/08-async-await/01-rewrite-async/solution.md
+++ b/1-js/11-async/08-async-await/01-rewrite-async/solution.md
@@ -19,7 +19,7 @@ loadJson('no-such-user.json')
 
 Notes:
 
-1. The function `loadUrl` becomes `async`.
+1. The function `loadJson` becomes `async`.
 2. All `.then` inside are replaced with `await`.
 3. We can `return response.json()` instead of awaiting for it, like this:
 
diff --git a/1-js/12-generators-iterators/2-async-iterators-generators/article.md b/1-js/12-generators-iterators/2-async-iterators-generators/article.md
index 45cf73938..43b214a0f 100644
--- a/1-js/12-generators-iterators/2-async-iterators-generators/article.md
+++ b/1-js/12-generators-iterators/2-async-iterators-generators/article.md
@@ -310,7 +310,7 @@ async function* fetchCommits(repo) {
 
 1. We use the browser `fetch` method to download from a remote URL. It allows to supply authorization and other headers if needed, here GitHub requires `User-Agent`.
 2. The fetch result is parsed as JSON, that's again a `fetch`-specific method.
-3. We can get the next page URL from the `Link` header of the response. It has a special format, so we use a regexp for that. The next page URL may look like this: `https://api.github.com/repositories/93253246/commits?page=2`, it's generatd by GitHub itself.
+3. We can get the next page URL from the `Link` header of the response. It has a special format, so we use a regexp for that. The next page URL may look like this: `https://api.github.com/repositories/93253246/commits?page=2`, it's generated by GitHub itself.
 4. Then we yield all commits received, and when they finish -- the next `while(url)` iteration will trigger, making one more request.
 
 An example of use (shows commit authors in console):
diff --git a/1-js/13-modules/01-modules-intro/article.md b/1-js/13-modules/01-modules-intro/article.md
index ad4f21068..6bf66abbf 100644
--- a/1-js/13-modules/01-modules-intro/article.md
+++ b/1-js/13-modules/01-modules-intro/article.md
@@ -6,7 +6,7 @@ A module usually contains a class or a library of useful functions.
 
 For a long time, JavaScript existed without a language-level module syntax. That wasn't a problem, because initially scripts were small and simple. So there was no need.
 
-But eventually scripts became more and more complex, so the community invented a variety of ways to organize code into modules.
+But eventually scripts became more and more complex, so the community invented a variety of ways to organize code into modules, special libraries to load modules on demand.
 
 For instance:
 
@@ -20,9 +20,9 @@ Now all these slowly become a part of history, but we still can find them in old
 
 A module is just a file, a single script, as simple as that.
 
-Directives `export` and `import` allow to interchange functionality between modules:
+There are directives `export` and `import` to interchange functionality between modules, call functions of one module from another one:
 
-- `export` keyword labels variables and functions that should be accessible from outside the file.
+- `export` keyword labels variables and functions that should be accessible from outside the current module.
 - `import` allows to import functionality from other modules.
 
 For instance, if we have a file `sayHi.js` exporting a function:
@@ -44,13 +44,15 @@ alert(sayHi); // function...
 sayHi('John'); // Hello, John!
 ```
 
-In this tutorial we concentrate on the language itself, but we use browser as the demo environment, so let's see how modules work in the browser.
+In this tutorial we concentrate on the language itself, but we use browser as the demo environment, so let's see how to use modules in the browser.
 
-To use modules, we must set the attribute `<script type="module">`, like this:
+As modules support special keywords and features, we must tell the browser that a script should be treated as module, by using the attribute `<script type="module">`.
+
+Like this:
 
 [codetabs src="say" height="140" current="index.html"]
 
-The browser automatically fetches and evaluates imports, then runs the script.
+The browser automatically fetches and evaluates imported modules, and then runs the script.
 
 ## Core module features
 
@@ -60,7 +62,7 @@ There are core features, valid both for browser and server-side JavaScript.
 
 ### Always "use strict"
 
-Modules always `use strict`. E.g. assigning to an undeclared variable will give an error.
+Modules always `use strict`, by default. E.g. assigning to an undeclared variable will give an error.
 
 ```html run
 <script type="module">
@@ -86,7 +88,7 @@ That's the correct variant:
 
 [codetabs src="scopes-working" height="140" current="hello.js"]
 
-In the browser, independant top-level scope also exists for each `<script type="module">`:
+In the browser, independent top-level scope also exists for each `<script type="module">`:
 
 ```html run
 <script type="module">
@@ -101,7 +103,7 @@ In the browser, independant top-level scope also exists for each `<script type="
 </script>
 ```
 
-If we really need to make a "global" in-browser variable, we can explicitly assign it to `window` and access as `window.user`. But that's an exception requiring a good reason.
+If we really need to make a window-level global variable, we can explicitly assign it to `window` and access as `window.user`. But that's an exception requiring a good reason.
 
 ### A module code is evaluated only the first time when imported
 
@@ -229,11 +231,11 @@ You may want skip those for now if you're reading for the first time, or if you
 Module scripts are *always* deferred, same effect as `defer` attribute (described in the chapter [](info:script-async-defer)), for both external and inline scripts.
 
 In other words:
-- external module scripts `<script type="module" src="...">` don't block HTML processing.
-- module scripts wait until the HTML document is fully ready.
-- relative order is maintained: scripts that go first in the document, execute first.
+- external module scripts `<script type="module" src="...">` don't block HTML processing, they load in parallel with other resources.
+- module scripts wait until the HTML document is fully ready (even if they are tiny and load faster than HTML), and then run.
+- relative order of scripts is maintained: scripts that go first in the document, execute first.
 
-As a side-effect, module scripts always see HTML elements below them.
+As a side-effect, module scripts always "see" the fully loaded HTML-page, including HTML elements below them.
 
 For instance:
 
@@ -245,6 +247,8 @@ For instance:
   // as modules are deferred, the script runs after the whole page is loaded
 </script>
 
+Compare to regular script below:
+
 <script>
 *!*
   alert(typeof button); // Error: button is undefined, the script can't see elements below
@@ -259,11 +263,11 @@ Please note: the second script actually works before the first! So we'll see `un
 
 That's because modules are deferred, so way wait for the document to be processed. The regular scripts runs immediately, so we saw its output first.
 
-When using modules, we should be aware that HTML-document can show up before the JavaScript application is ready. Some functionality may not work yet. We should put transparent overlays or "loading indicators", or otherwise ensure that the visitor won't be confused because of it.
+When using modules, we should be aware that HTML-page shows up as it loads, and JavaScript modules run after that, so the user may see the page before the JavaScript application is ready. Some functionality may not work yet. We should put transparent overlays or "loading indicators", or otherwise ensure that the visitor won't be confused by that.
 
 ### Async works on inline scripts
 
-Async attribute `<script async type="module">` is allowed on both inline and external scripts. Async scripts run immediately when imported modules are processed, independantly of other scripts or the HTML document.
+Async attribute `<script async type="module">` is allowed on both inline and external scripts. Async scripts run immediately when imported modules are processed, independently of other scripts or the HTML document.
 
 For example, the script below has `async`, so it doesn't wait for anyone.
 
@@ -301,17 +305,17 @@ There are two notable differences of external module scripts:
 
     That ensures better security by default.
 
-### No bare modules allowed
+### No "bare" modules allowed
 
-In the browser, in scripts (not in HTML), `import` must get either a relative or absolute URL. So-called "bare" modules, without a path, are not allowed.
+In the browser, `import` must get either a relative or absolute URL. Modules without any path are called "bare" modules. Such modules are not allowed in `import`.
 
 For instance, this `import` is invalid:
 ```js
 import {sayHi} from 'sayHi'; // Error, "bare" module
-// must be './sayHi.js' or wherever the module is
+// the module must have a path, e.g. './sayHi.js' or wherever the module is
 ```
 
-Certain environments, like Node.js or bundle tools allow bare modules, as they have own ways for finding modules and hooks to fine-tune them. But browsers do not support bare modules yet.
+Certain environments, like Node.js or bundle tools allow bare modules, without any path, as they have own ways for finding modules and hooks to fine-tune them. But browsers do not support bare modules yet.
 
 ### Compatibility, "nomodule"
 
@@ -328,7 +332,7 @@ Old browsers do not understand `type="module"`. Scripts of the unknown type are
 </script>
 ```
 
-If we use bundle tools, then as modules are bundled together, their `import/export` statements are replaced by special bundler calls, so the resulting build does not require `type="module"`, and we can put it into a regular script:
+If we use bundle tools, then as scripts are bundled together into a single file (or few files), `import/export` statements inside those scripts are replaced by special bundler functions. So the resulting "bundled" script does not contain any `import/export`, it doesn't require `type="module"`, and we can put it into a regular script:
 
 ```html
 <!-- Assuming we got bundle.js from a tool like Webpack -->
@@ -362,7 +366,7 @@ To summarize, the core concepts are:
 1. A module is a file. To make `import/export` work, browsers need `<script type="module">`, that implies several differences:
     - Deferred by default.
     - Async works on inline scripts.
-    - External scripts need CORS headers.
+    - To load external scripts from another origin (domain/protocol/port), CORS headers are needed.
     - Duplicate external scripts are ignored.
 2. Modules have their own, local top-level scope and interchange functionality via `import/export`.
 3. Modules always `use strict`.
diff --git a/1-js/13-modules/02-import-export/article.md b/1-js/13-modules/02-import-export/article.md
index bf31065bc..8aa122f07 100644
--- a/1-js/13-modules/02-import-export/article.md
+++ b/1-js/13-modules/02-import-export/article.md
@@ -1,4 +1,3 @@
-
 # Export and Import
 
 Export and import directives are very versatile.
@@ -104,7 +103,7 @@ Well, there are few reasons.
     export function becomeSilent() { ... }
     ```
 
-    Now if we in fact need only one of them in our project:
+    Now if we only use one of `lib.js` functions in our project:
     ```js
     // 📁 main.js
     import {sayHi} from './lib.js';
@@ -219,8 +218,7 @@ export default function(user) { // no function name
 export default ['Jan', 'Feb', 'Mar','Apr', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];
 ```
 
-That's fine, because `export default` is only one per file, so `import` always knows what to import.
- Contrary to that, omitting a name for named imports would be an error:
+That's fine, because `export default` is only one per file. Contrary to that, omitting a name for named imports would be an error:
 
 ```js
 export class { // Error! (non-default export needs a name)
@@ -230,9 +228,9 @@ export class { // Error! (non-default export needs a name)
 
 ### "Default" alias
 
-The "default" word is a kind of "alias" for the default export, for scenarios when we need to reference it somehow.
+The "default" keyword is used as an "alias" for the default export, for standalone exports and other scenarios when we need to reference it.
 
-For example, if we already have a function declared, that's how to `export default` it:
+For example, if we already have a function declared, that's how to `export default` it (separately from the definition):
 
 ```js
 function sayHi(user) {
@@ -279,7 +277,7 @@ new User('John');
 
 ### Should I use default exports?
 
-One should be careful about using default exports, because they are somewhat more different to maintain.
+One should be careful about using default exports, because they are more difficult to maintain.
 
 Named exports are explicit. They exactly name what they import, so we have that information from them, that's a good thing.
 
@@ -287,12 +285,15 @@ Also, named exports enforce us to use exactly the right name to import:
 
 ```js
 import {User} from './user.js';
+// import {MyUser} won't work, the name must be {User}
 ```
 
-For default exports, we need to create a name on our own:
+For default exports, we always choose the name when importing:
 
 ```js
-import MyUser from './user.js'; // could be import Anything..., and it'll work
+import User from './user.js'; // works
+import MyUser from './user.js'; // works too
+// could be import Anything..., and it'll be work
 ```
 
 So, there's a little bit more freedom that can be abused, so that team members may use different names for the same thing.
@@ -377,7 +378,7 @@ export {default as Github} from './providers/github.js';
 ````warn header="Re-exporting default is tricky"
 Please note: `export User from './user.js'` won't work. It's actually a syntax error. To re-export the default export, we must mention it explicitly `{default as ...}`, like in the example above.
 
-Also, there's another oddity: `export * from './user.js'` re-exports only named exports, exluding the default one. Once again, we need to mention it explicitly.
+Also, there's another oddity: `export * from './user.js'` re-exports only named exports, excluding the default one. Once again, we need to mention it explicitly.
 
 For instance, to re-export everything, two statements will be necessary:
 ```js
@@ -410,16 +411,18 @@ Import:
   - `import {default as x} from "mod"`
 - Everything:
   - `import * as obj from "mod"`
-- Only fetch/evalute the module, don't import:
+- Import the module (it runs), but do not assign it to a variable:
   - `import "mod"`
 
-We can put import/export statements below or after other code, that doesn't matter.
+We can put import/export statements at the top or at the bottom of a script, that doesn't matter.
 
 So this is technically fine:
 ```js
 sayHi();
 
-import {sayHi} from './say.js'; // import at the end of the file
+// ...
+
+import {sayHi} from './say.js'; // import at the end of the script
 ```
 
 In practice imports are usually at the start of the file, but that's only for better convenience.
diff --git a/1-js/13-modules/03-modules-dynamic-imports/article.md b/1-js/13-modules/03-modules-dynamic-imports/article.md
index d8de2bcfa..5d2538729 100644
--- a/1-js/13-modules/03-modules-dynamic-imports/article.md
+++ b/1-js/13-modules/03-modules-dynamic-imports/article.md
@@ -5,7 +5,7 @@ Export and import statements that we covered in previous chaters are called "sta
 
 That's because they are indeed static. The syntax is very strict.
 
-First, we can't dynamicaly generate any parameters of `import`.
+First, we can't dynamically generate any parameters of `import`.
 
 The module path must be a primitive string, can't be a function call. This won't work:
 
diff --git a/10-misc/12-mutation-observer/article.md b/10-misc/12-mutation-observer/article.md
index 1045e87a8..552c2a890 100644
--- a/10-misc/12-mutation-observer/article.md
+++ b/10-misc/12-mutation-observer/article.md
@@ -35,10 +35,10 @@ Then after any changes, the `callback` is executed, with a list of [MutationReco
 [MutationRecord](https://dom.spec.whatwg.org/#mutationrecord) objects have properties:
 
 - `type` -- mutation type, one of
-    - `"attributes"` (attribute modified)
-    - `"characterData"` (data modified)
-    - `"childList"` (elements added/removed),
-- `target` -- where the change occured: an element for "attributes", or text node for "characterData", or an element for a "childList" mutation,
+    - `"attributes"`: attribute modified
+    - `"characterData"`: data modified, used for text nodes,
+    - `"childList"`: child elements added/removed,
+- `target` -- where the change occurred: an element for "attributes", or text node for "characterData", or an element for a "childList" mutation,
 - `addedNodes/removedNodes`  -- nodes that were added/removed,
 - `previousSibling/nextSibling` -- the previous and next sibling to added/removed nodes,
 - `attributeName/attributeNamespace` -- the name/namespace (for XML) of the changed attribute,
@@ -48,7 +48,7 @@ Then after any changes, the `callback` is executed, with a list of [MutationReco
 For example, here's a `<div>` with `contentEditable` attribute. That attribute allows us to focus on it and edit.
 
 ```html run
-<div contentEditable id="elem">Edit <b>me</b>, please</div>
+<div contentEditable id="elem">Click and <b>edit</b>, please</div>
 
 <script>
 let observer = new MutationObserver(mutationRecords => {
@@ -98,11 +98,11 @@ mutationRecords = [{
 
 When `MutationObserver` is needed? Is there a scenario when such thing can be useful?
 
-Sure, we can track something like `contentEditable` and create "undo/redo" stack, but here's  an example where `MutationObserver` is good from architectural standpoint.
+We can track something like `contentEditable` and implement "undo/redo" functionality (record mutations and rollback/redo them on demand). There are also cases when `MutationObserver` is good from architectural standpoint.
 
-Let's say we're making a website about programming, like this one. Naturally, articles and other materials may contain source code snippets.
+Let's say we're making a website about programming. Naturally, articles and other materials may contain source code snippets.
 
-An HTML code snippet looks like this:
+An HTML markup of a code snippet looks like this:
 ```html
 ...
 <pre class="language-javascript"><code>
@@ -112,9 +112,9 @@ An HTML code snippet looks like this:
 ...
 ```
 
-There's also a JavaScript highlighting library, e.g. [Prism.js](https://prismjs.com/). A call to `Prism.highlightElem(pre)` examines the contents of such `pre` elements and adds colored syntax highlighting, similar to what you in examples here, this page.
+Also we'll use a JavaScript highlighting library on our site, e.g. [Prism.js](https://prismjs.com/). A call to `Prism.highlightElem(pre)` examines the contents of such `pre` elements and adds into them special tags and styles for colored syntax highlighting, similar to what you see in examples here, at this page.
 
-Generally, when a page loads, e.g. at the bottom of the page, we can search for elements `pre[class*="language"]` and call `Prism.highlightElem` on them:
+When to run that method? We can do it on `DOMContentLoaded` event, or at the bottom of the page. At that moment we have DOM ready, can search for elements `pre[class*="language"]` and call `Prism.highlightElem` on them:
 
 ```js
 // highlight all code snippets on the page
@@ -139,7 +139,7 @@ articleElem.innerHTML = article;
 
 The new `article` HTML may contain code snippets. We need to call `Prism.highlightElem` on them, otherwise they won't get highlighted.
 
-**Who's responsibility is to call `Prism.highlightElem` for a dynamically loaded article?**
+**Where and when to call `Prism.highlightElem` for a dynamically loaded article?**
 
 We could append that call to the code that loads an article, like this:
 
@@ -153,9 +153,9 @@ snippets.forEach(Prism.highlightElem);
 */!*
 ```
 
-...But imagine, we have many places where we load contents with code: articles, quizzes, forum posts. Do we need to put the highlighting call everywhere? Then we need to be careful, not to forget about it.
+...But imagine, we have many places in the code where we load contents: articles, quizzes, forum posts. Do we need to put the highlighting call everywhere? That's not very convenient, and also easy to forget.
 
-And what if we load the content into a third-party engine? E.g. we have a forum written by someone else, that loads contents dynamically, and we'd like to add syntax highlighting to it. No one likes to patch third-party scripts.
+And what if the content is loaded by a third-party module? E.g. we have a forum written by someone else, that loads contents dynamically, and we'd like to add syntax highlighting to it. No one likes to patch third-party scripts.
 
 Luckily, there's another option.
 
@@ -176,7 +176,7 @@ let observer = new MutationObserver(mutations => {
     // examine new nodes
 
     for(let node of mutation.addedNodes) {
-      // skip newly added text nodes
+      // we track only elements, skip other nodes (e.g. text nodes)
       if (!(node instanceof HTMLElement)) continue;
 
       // check the inserted element for being a code snippet
@@ -184,7 +184,7 @@ let observer = new MutationObserver(mutations => {
         Prism.highlightElement(node);
       }
 
-      // search its subtree for code snippets
+      // maybe there's a code snippet somewhere in its subtree?
       for(let elem of node.querySelectorAll('pre[class*="language-"]')) {
         Prism.highlightElement(elem);
       }
@@ -200,7 +200,7 @@ observer.observe(demoElem, {childList: true, subtree: true});
 
 <p id="highlight-demo" style="border: 1px solid #ddd">Demo element with <code>id="highlight-demo"</code>, obverved by the example above.</p>
 
-The code below populates `innerHTML`. If you've run the code above, snippets will get highlighted:
+The code below populates `innerHTML`. Please run the code above first, it will watch and highlight the new content:
 
 ```js run
 let demoElem = document.getElementById('highlight-demo');
@@ -217,12 +217,9 @@ demoElem.innerHTML = `A code snippet is below:
 
 Now we have `MutationObserver` that can track all highlighting in observed elements or the whole `document`. We can add/remove code snippets in HTML without thinking about it.
 
+## Additional methods
 
-## Garbage collection
-
-Observers use weak references to nodes internally. That is: if a node is removed from DOM, and becomes unreachable, then it becomes garbage collected, an observer doesn't prevent that.
-
-Still, we can release observers any time:
+There's a method to stop observing the node:
 
 - `observer.disconnect()` -- stops the observation.
 
@@ -240,6 +237,10 @@ let mutationRecords = observer.takeRecords();
 observer.disconnect();
 ```
 
+## Garbage collection
+
+Observers use weak references to nodes internally. That is: if a node is removed from DOM, and becomes unreachable, then it becomes garbage collected, an observer doesn't prevent that.
+
 ## Summary  
 
 `MutationObserver` can react on changes in DOM: attributes, added/removed elements, text content.
diff --git a/2-ui/1-document/02-dom-nodes/article.md b/2-ui/1-document/02-dom-nodes/article.md
index 6bb34ff8c..c496b16d1 100644
--- a/2-ui/1-document/02-dom-nodes/article.md
+++ b/2-ui/1-document/02-dom-nodes/article.md
@@ -106,7 +106,7 @@ drawHtmlTree(node3, 'div.domtree', 690, 150);
 
 While generating the DOM, browsers automatically process errors in the document, close tags and so on.
 
-Such an "invalid" document:
+Such an document with unclosed tags:
 
 ```html no-beautify
 <p>Hello
@@ -225,7 +225,7 @@ The best way to study them is to click around. Most values are editable in-place
 
 ## Interaction with console
 
-As we explore the DOM, we also may want to apply JavaScript to it. Like: get a node and run some code to modify it, to see how it looks. Here are few tips to travel between the Elements tab and the console.
+As we explore the DOM, we also may want to apply JavaScript to it. Like: get a node and run some code to modify it, to see the result. Here are few tips to travel between the Elements tab and the console.
 
 - Select the first `<li>` in the Elements tab.
 - Press `key:Esc` -- it will open console right below the Elements tab.
diff --git a/2-ui/1-document/03-dom-navigation/3-navigation-links-which-null/solution.md b/2-ui/1-document/03-dom-navigation/3-navigation-links-which-null/solution.md
index e962eb662..266d26b1b 100644
--- a/2-ui/1-document/03-dom-navigation/3-navigation-links-which-null/solution.md
+++ b/2-ui/1-document/03-dom-navigation/3-navigation-links-which-null/solution.md
@@ -1,4 +1,6 @@
-1. Yes, true. The element `elem.lastChild` is always the last one, it has no `nextSibling`, so if there are children, then yes.
-2. No, wrong, because `elem.children[0]` is the first child among elements. But there may be non-element nodes before it. So `previousSibling` may be a text node.
+1. Yes, true. The element `elem.lastChild` is always the last one, it has no `nextSibling`.
+2. No, wrong, because `elem.children[0]` is the first child *among elements*. But there may exist non-element nodes before it. So `previousSibling` may be a text node. Also, if there are no children, then trying to access `elem.children[0]`
 
-Please note that for both cases if there are no children, then there will be an error. For instance, if `elem.lastChild` is `null`, we can't access `elem.lastChild.nextSibling`.
+Please note: for both cases if there are no children, then there will be an error.
+
+If there are no children, `elem.lastChild` is `null`, so we can't access `elem.lastChild.nextSibling`. And the collection `elem.children` is empty (like an empty array `[]`).
diff --git a/2-ui/1-document/03-dom-navigation/article.md b/2-ui/1-document/03-dom-navigation/article.md
index 1e1e4058c..be5a6531b 100644
--- a/2-ui/1-document/03-dom-navigation/article.md
+++ b/2-ui/1-document/03-dom-navigation/article.md
@@ -7,7 +7,7 @@ libs:
 
 # Walking the DOM
 
-The DOM allows us to do anything with elements and their contents, but first we need to reach the corresponding DOM object, get it into a variable, and then we are able to modify it.
+The DOM allows us to do anything with elements and their contents, but first we need to reach the corresponding DOM object.
 
 All operations on the DOM start with the `document` object. From it we can access any node.
 
@@ -86,7 +86,7 @@ For instance, here `<body>` has children `<div>` and `<ul>` (and few blank text
 </html>
 ```
 
-...And if we ask for all descendants of `<body>`, then we get direct children `<div>`, `<ul>` and also more nested elements like `<li>` (being a child of `<ul>`) and `<b>` (being a child of `<li>`) -- the entire subtree.
+...And all descendants of `<body>` are not only direct children `<div>`, `<ul>` but also more deeply nested elements, such as `<li>` (a child of `<ul>`) and `<b>` (a child of `<li>`) -- the entire subtree.
 
 **The `childNodes` collection provides access to all child nodes, including text nodes.**
 
diff --git a/2-ui/1-document/04-searching-elements-dom/article.md b/2-ui/1-document/04-searching-elements-dom/article.md
index 18ce24eba..b5dbba50d 100644
--- a/2-ui/1-document/04-searching-elements-dom/article.md
+++ b/2-ui/1-document/04-searching-elements-dom/article.md
@@ -35,7 +35,7 @@ If we declare a variable with the same name, it takes precedence:
 <script>
   let elem = 5;
 
-  alert(elem); // the variable overrides the element
+  alert(elem); // 5
 </script>
 ```
 
@@ -172,7 +172,7 @@ Today, they are mostly history, as `querySelector` is more powerful and shorter
 So here we cover them mainly for completeness, while you can still find them in the old scripts.
 
 - `elem.getElementsByTagName(tag)` looks for elements with the given tag and returns the collection of them. The `tag` parameter can also be a star `"*"` for "any tags".
-- `elem.getElementsByClassName(className)` returns elements that have the given CSS class. Elements may have other classes too.
+- `elem.getElementsByClassName(className)` returns elements that have the given CSS class.
 - `document.getElementsByName(name)` returns elements with the given `name` attribute, document-wide. very rarely used.
 
 For instance:
@@ -305,8 +305,6 @@ If we use it instead, then both scripts output `1`:
 
 Now we can easily see the difference. The static collection did not increase after the appearance of a new `div` in the document.
 
-Here we used separate scripts to illustrate how the element addition affects the collection, but any DOM manipulations affect them. Soon we'll see more of them.
-
 ## Summary
 
 There are 6 main methods to search for nodes in DOM:
@@ -367,5 +365,5 @@ Besides that:
 - There is `elem.matches(css)` to check if `elem` matches the given CSS selector.
 - There is `elem.closest(css)` to look for the nearest ancestor that matches the given CSS-selector. The `elem` itself is also checked.
 
-And let's mention one more method here to check for the child-parent relationship:
+And let's mention one more method here to check for the child-parent relationship, as it's sometimes useful:
 -  `elemA.contains(elemB)` returns true if `elemB` is inside `elemA` (a descendant of `elemA`) or when `elemA==elemB`.
diff --git a/2-ui/1-document/06-dom-attributes-and-properties/article.md b/2-ui/1-document/06-dom-attributes-and-properties/article.md
index c1bcf2ce1..83beeabac 100644
--- a/2-ui/1-document/06-dom-attributes-and-properties/article.md
+++ b/2-ui/1-document/06-dom-attributes-and-properties/article.md
@@ -186,7 +186,7 @@ In the example above:
 - Changing the attribute `value` updates the property.
 - But the property change does not affect the attribute.
 
-That "feature" may actually come in handy, because the user may modify `value`, and then after it, if we want to recover the "original" value from HTML, it's in the attribute.
+That "feature" may actually come in handy, because the user actions may lead to `value` changes, and then after them, if we want to recover the "original" value from HTML, it's in the attribute.
 
 ## DOM properties are typed
 
@@ -216,9 +216,9 @@ There are other examples. The `style` attribute is a string, but the `style` pro
 </script>
 ```
 
-That's an important difference. But even if a DOM property type is a string, it may differ from the attribute!
+Most properties are strings though.
 
-For instance, the `href` DOM property is always a *full* URL, even if the attribute contains a relative URL or just a `#hash`.
+Quite rarely, even if a DOM property type is a string, it may differ from the attribute. For instance, the `href` DOM property is always a *full* URL, even if the attribute contains a relative URL or just a `#hash`.
 
 Here's an example:
 
@@ -380,7 +380,7 @@ Methods to work with attributes are:
 - `elem.removeAttribute(name)` -- to remove the attribute.
 - `elem.attributes` is a collection of all attributes.
 
-For most needs, DOM properties can serve us well. We should refer to attributes only when DOM properties do not suit us, when we need exactly attributes, for instance:
+For most situations using DOM properties is preferable. We should refer to attributes only when DOM properties do not suit us, when we need exactly attributes, for instance:
 
 - We need a non-standard attribute. But if it starts with `data-`, then we should use `dataset`.
 - We want to read the value "as written" in HTML. The value of the DOM property may be different, for instance the `href` property is always a full URL, and we may want to get the "original" value.
diff --git a/2-ui/1-document/07-modifying-document/1-createtextnode-vs-innerhtml/solution.md b/2-ui/1-document/07-modifying-document/1-createtextnode-vs-innerhtml/solution.md
index 93ae862fd..a38f01645 100644
--- a/2-ui/1-document/07-modifying-document/1-createtextnode-vs-innerhtml/solution.md
+++ b/2-ui/1-document/07-modifying-document/1-createtextnode-vs-innerhtml/solution.md
@@ -12,7 +12,7 @@ Here's an example:
   let text = '<b>text</b>';
 
   elem1.append(document.createTextNode(text));
-  elem2.textContent = text;
-  elem3.innerHTML = text;
+  elem2.innerHTML = text;
+  elem3.textContent = text;
 </script>
 ```
diff --git a/2-ui/2-events/01-introduction-browser-events/02-hide-self-onclick/solution.md b/2-ui/2-events/01-introduction-browser-events/02-hide-self-onclick/solution.md
index ec2806696..cded5b622 100644
--- a/2-ui/2-events/01-introduction-browser-events/02-hide-self-onclick/solution.md
+++ b/2-ui/2-events/01-introduction-browser-events/02-hide-self-onclick/solution.md
@@ -1,4 +1,4 @@
-Can use `this` in the handler to reference "itself" here:
+Can use `this` in the handler to reference "the element itself" here:
 
 ```html run height=50
 <input type="button" onclick="this.hidden=true" value="Click to hide">
diff --git a/2-ui/2-events/01-introduction-browser-events/04-move-ball-field/solution.md b/2-ui/2-events/01-introduction-browser-events/04-move-ball-field/solution.md
index bda48e2bb..00de64008 100644
--- a/2-ui/2-events/01-introduction-browser-events/04-move-ball-field/solution.md
+++ b/2-ui/2-events/01-introduction-browser-events/04-move-ball-field/solution.md
@@ -36,7 +36,7 @@ To get field-relative `left` coordinate of the click, we can substract the field
 let left = event.clientX - fieldCoords.left - field.clientLeft;
 ```
 
-Normally, `ball.style.position.left` means the "left edge of the element" (the ball). So if we assign that `left`, then the ball edge would be under the mouse cursor.
+Normally, `ball.style.position.left` means the "left edge of the element" (the ball). So if we assign that `left`, then the ball edge, not center, would be under the mouse cursor.
 
 We need to move the ball half-width left and half-height up to make it center.
 
diff --git a/2-ui/2-events/01-introduction-browser-events/05-sliding-menu/solution.md b/2-ui/2-events/01-introduction-browser-events/05-sliding-menu/solution.md
index eed096231..7554a2f09 100644
--- a/2-ui/2-events/01-introduction-browser-events/05-sliding-menu/solution.md
+++ b/2-ui/2-events/01-introduction-browser-events/05-sliding-menu/solution.md
@@ -29,7 +29,7 @@ Like this:
 
 So if we set `onclick` on it, then it will catch clicks to the right of the text.
 
-...but `<span>` has an implicit `display: inline`, so it occupies exactly enough place to fit all the text:
+As `<span>` has an implicit `display: inline`, it occupies exactly enough place to fit all the text:
 
 ```html autorun height=50
 <span style="border: solid red 1px" onclick="alert(1)">Sweeties (click me)!</span>
diff --git a/2-ui/2-events/01-introduction-browser-events/article.md b/2-ui/2-events/01-introduction-browser-events/article.md
index 332d15793..ee69e9df2 100644
--- a/2-ui/2-events/01-introduction-browser-events/article.md
+++ b/2-ui/2-events/01-introduction-browser-events/article.md
@@ -160,9 +160,9 @@ button.onclick = sayThanks;
 button.onclick = sayThanks();
 ```
 
-If we add brackets, then `sayThanks()` --  will be the *result* of the function execution, so `onclick` in the last code becomes `undefined` (the function returns nothing). That won't work.
+If we add parentheses, `sayThanks()` --  is a function call. So the last line actually takes the *result* of the function execution, that is `undefined` (as the function returns nothing), and assigns it to `onclick`. That doesn't work.
 
-...But in the markup we do need the brackets:
+...But in the markup we do need the parentheses:
 
 ```html
 <input type="button" id="button" onclick="sayThanks()">
@@ -228,7 +228,7 @@ element.addEventListener(event, handler[, options]);
 `options`
 : An additional optional object with properties:
     - `once`: if `true`, then the listener is automatically removed after it triggers.
-    - `capture`: the phrase where to handle the event, to be covered later in the chapter <info:bubbling-and-capturing>. For historical reasons, `options` can also be `false/true`, that's the same as `{capture: false/true}`.
+    - `capture`: the phase where to handle the event, to be covered later in the chapter <info:bubbling-and-capturing>. For historical reasons, `options` can also be `false/true`, that's the same as `{capture: false/true}`.
     - `passive`: if `true`, then the handler will not `preventDefault()`, we'll cover that later in <info:default-browser-action>.
 
 
@@ -351,7 +351,7 @@ Some properties of `event` object:
 : Event type, here it's `"click"`.
 
 `event.currentTarget`
-: Element that handled the event. That's exactly the same as `this`, unless you bind `this` to something else, and then `event.currentTarget` becomes useful.
+: Element that handled the event. That's exactly the same as `this`, unless the handler is an arrow function, or its `this` is bound to something else, then `event.currentTarget` becomes useful.
 
 `event.clientX / event.clientY`
 : Window-relative coordinates of the cursor, for mouse events.
diff --git a/2-ui/2-events/04-default-browser-action/article.md b/2-ui/2-events/04-default-browser-action/article.md
index 44355de0d..ea9bab2cb 100644
--- a/2-ui/2-events/04-default-browser-action/article.md
+++ b/2-ui/2-events/04-default-browser-action/article.md
@@ -236,7 +236,7 @@ If the default action was prevented, the value of `event.defaultPrevented` becom
 ```warn header="Stay semantic, don't abuse"
 Technically, by preventing default actions and adding JavaScript we can customize the behavior of any elements. For instance, we can make a link `<a>` work like a button, and a button `<button>` behave as a link (redirect to another URL or so).
 
-But we should generally keep the semantic meaning of HTML elements. For instance, `<a>` should preform navigation, not a button.
+But we should generally keep the semantic meaning of HTML elements. For instance, `<a>` should perform navigation, not a button.
 
 Besides being "just a good thing", that makes your HTML better in terms of accessibility.
 
diff --git a/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/1-behavior-nested-tooltip/solution.view/index.html b/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/1-behavior-nested-tooltip/solution.view/index.html
index c8e879f2c..e998165fd 100644
--- a/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/1-behavior-nested-tooltip/solution.view/index.html
+++ b/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/1-behavior-nested-tooltip/solution.view/index.html
@@ -78,12 +78,13 @@
     }
 
     document.onmouseout = function() {
-      // it is possible that mouseout triggered, but we're still inside the element (cause of bubbling)
+      // it is possible that mouseout triggered, but we're still inside the element
+      // (its target was inside, and it bubbled)
       // but in this case we'll have an immediate mouseover,
       // so the tooltip will be destroyed and shown again
       //
-      // that's an overhead, but here it's not visible
-      // can be fixed with additional checks
+      // luckily, the "blinking" won't be visible,
+      // as both events happen almost at the same time
       if (tooltip) {
         tooltip.remove();
         tooltip = false;
diff --git a/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/2-hoverintent/source.view/index.html b/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/2-hoverintent/source.view/index.html
index 702b79f96..856daf3a8 100644
--- a/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/2-hoverintent/source.view/index.html
+++ b/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/2-hoverintent/source.view/index.html
@@ -1,5 +1,5 @@
 <!doctype html>
-<html lang="en">
+<html>
 
 <head>
   <meta charset="UTF-8">
diff --git a/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/2-hoverintent/task.md b/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/2-hoverintent/task.md
index 3dfb7e9e1..83ceb9445 100644
--- a/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/2-hoverintent/task.md
+++ b/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/2-hoverintent/task.md
@@ -13,7 +13,7 @@ Technically, we can measure the mouse speed over the element, and if it's slow t
 Make a universal object `new HoverIntent(options)` for it. With `options`:
 
 - `elem` -- element to track.
-- `over` -- a function to call if the mouse is slowly moving the element.
+- `over` -- a function to call if the mouse is slowly moving over the element.
 - `out` -- a function to call when the mouse leaves the element (if `over` was called).
 
 An example of using such object for the tooltip:
diff --git a/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/article.md b/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/article.md
index f60d7e63e..6812d99a5 100644
--- a/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/article.md
+++ b/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/article.md
@@ -10,15 +10,17 @@ The `mouseover` event occurs when a mouse pointer comes over an element, and `mo
 
 These events are special, because they have a `relatedTarget`.
 
+This property complements `target`. When a mouse leaves one element for another, one of them becomes `target`, and the other one `relatedTarget`.
+
 For `mouseover`:
 
 - `event.target` -- is the element where the mouse came over.
-- `event.relatedTarget` -- is the element from which the mouse came.
+- `event.relatedTarget` -- is the element from which the mouse came (`relatedTarget` -> `target`).
 
 For `mouseout` the reverse:
 
 - `event.target` -- is the element that mouse left.
-- `event.relatedTarget` -- is the new under-the-pointer element (that mouse left for).
+- `event.relatedTarget` -- is the new under-the-pointer element, that mouse left for (`target` -> `relatedTarget`).
 
 ```online
 In the example below each face feature is an element. When you move the mouse, you can see mouse events in the text area.
diff --git a/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/mouseoverout-fast.view/index.html b/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/mouseoverout-fast.view/index.html
index 1e38d693c..17239b026 100755
--- a/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/mouseoverout-fast.view/index.html
+++ b/2-ui/3-event-details/3-mousemove-mouseover-mouseout-mouseenter-mouseleave/mouseoverout-fast.view/index.html
@@ -1,5 +1,5 @@
 <!doctype html>
-<html lang="en">
+<html>
 
 <head>
   <meta charset="UTF-8">
diff --git a/2-ui/3-event-details/4-mouse-drag-and-drop/article.md b/2-ui/3-event-details/4-mouse-drag-and-drop/article.md
index 6390b392a..2c781c59f 100644
--- a/2-ui/3-event-details/4-mouse-drag-and-drop/article.md
+++ b/2-ui/3-event-details/4-mouse-drag-and-drop/article.md
@@ -101,7 +101,7 @@ ball.style.left = pageX - ball.offsetWidth / 2 + 'px';
 ball.style.top = pageY - ball.offsetHeight / 2 + 'px';
 ```
 
-Not bad, but there's a side-effect. To initiate the drag'n'drop can we `mousedown` anywhere on the ball. If do it at the edge, then the ball suddenly "jumps" to become centered.
+Not bad, but there's a side-effect. To initiate the drag'n'drop, we can `mousedown` anywhere on the ball. But if do it at the edge, then the ball suddenly "jumps" to become centered.
 
 It would be better if we keep the initial shift of the element relative to the pointer.
 
diff --git a/2-ui/3-event-details/5-keyboard-events/article.md b/2-ui/3-event-details/5-keyboard-events/article.md
index 7decd91be..afaa50bf1 100644
--- a/2-ui/3-event-details/5-keyboard-events/article.md
+++ b/2-ui/3-event-details/5-keyboard-events/article.md
@@ -75,13 +75,11 @@ Please note that `event.code` specifies exactly which key is pressed. For instan
 
 Let's say, we want to handle a hotkey: `key:Ctrl+Z` (or `key:Cmd+Z` for Mac). Most text editors hook the "Undo" action on it. We can set a listener on `keydown` and check which key is pressed -- to detect when we have the hotkey.
 
-Please answer the question -- in such a listener, should we check the value of `event.key` or `event.code`?
+There's a dilemma here: in such a listener, should we check the value of `event.key` or `event.code`?
 
-Please, pause and answer.
+On one hand, the value of `event.key` changes depending on the language. If the visitor has several languages in OS and switches between them, the same key gives different characters. So it makes sense to check `event.code`, it's always the same.
 
-Made up your mind?
-
-If you've got an understanding, then the answer is, of course, `event.code`, as we don't want `event.key` there. The value of `event.key` can change depending on the language or `CapsLock` enabled. The value of `event.code` is strictly bound to the key, so here we go:
+Like this:
 
 ```js run
 document.addEventListener('keydown', function(event) {
@@ -91,11 +89,30 @@ document.addEventListener('keydown', function(event) {
 });
 ```
 
+On the other hand, there's a problem with `event.code`. For different keyboard layouts, the same key may have different labels (letters).
+
+For example, here are US layout ("QWERTY") and German layout ("QWERTZ") under it (courtesy of Wikipedia):
+
+![](us-layout.png)
+
+![](german-layout.png)
+
+For the same key, US layout has "Z", while German layout has "Y" (letters are swapped).
+
+So, `event.code` will equal `KeyZ` for people with German layout when they press "Y".
+
+That sounds odd, but so it is. The [specification](https://www.w3.org/TR/uievents-code/#table-key-code-alphanumeric-writing-system) explicitly mentions such behavior.
+
+- `event.code` has the benefit of staying always the same, bound to the physical key location, even if the visitor changes languages. So hotkeys that rely on it work well even in case of a language switch.
+- `event.code` may match a wrong character for unexpected layout. Same letters in different layouts may map to different physical keys, leading to different codes. That happens for several codes, e.g. `keyA`, `keyQ`, `keyZ` (as we've seen). You can find the list in the [specification](https://www.w3.org/TR/uievents-code/#table-key-code-alphanumeric-writing-system).
+
+So, to reliably track layout-dependent characters, `event.key` may be a better way.
+
 ## Auto-repeat
 
-If a key is being pressed for a long enough time, it starts to repeat: the `keydown` triggers again and again, and then when it's released we finally get `keyup`. So it's kind of normal to have many `keydown` and a single `keyup`.
+If a key is being pressed for a long enough time, it starts to "auto-repeat": the `keydown` triggers again and again, and then when it's released we finally get `keyup`. So it's kind of normal to have many `keydown` and a single `keyup`.
 
-For all repeating keys the event object has `event.repeat` property set to `true`.
+For events triggered by auto-repeat, the event object has `event.repeat` property set to `true`.
 
 
 ## Default actions
@@ -146,10 +163,9 @@ Now arrows and deletion works well.
 
 In the past, there was a `keypress` event, and also `keyCode`, `charCode`, `which` properties of the event object.
 
-There were so many browser incompatibilities that developers of the specification decided to deprecate all of them. The old code still works, as the browser keep supporting them, but there's totally no need to use those any more.
-
-There was time when this chapter included their detailed description. But as of now we can forget about those.
+There were so many browser incompatibilities that developers of the specification decided to deprecate all of them. The old code still works, as browsers keep supporting them, but there's totally no need to use those any more.
 
+There was a time when this chapter included their detailed description. But as of now it was removed and replaced with more details about the modern event handling.
 
 ## Summary
 
@@ -165,6 +181,6 @@ Main keyboard event properties:
 - `code` -- the "key code" (`"KeyA"`, `"ArrowLeft"` and so on), specific to the physical location of the key on keyboard.
 - `key` -- the character (`"A"`, `"a"` and so on), for non-character keys usually has the same value  as `code`.
 
-In the past, keyboard events were sometimes used to track user input in form fields. That's not reliable, because the input can come from various sources. We have `input` and `change` events to handle any input (covered later in the chapter <info:events-change-input>). They trigger after any input, including mouse or speech recognition.
+In the past, keyboard events were sometimes used to track user input in form fields. That's not reliable, because the input can come from various sources. We have `input` and `change` events to handle any input (covered later in the chapter <info:events-change-input>). They trigger after any kind of input, including copy-pasting or speech recognition.
 
 We should use keyboard events when we really want keyboard. For example, to react on hotkeys or special keys.
diff --git a/2-ui/3-event-details/5-keyboard-events/german-layout.png b/2-ui/3-event-details/5-keyboard-events/german-layout.png
new file mode 100644
index 000000000..7e24f254e
Binary files /dev/null and b/2-ui/3-event-details/5-keyboard-events/german-layout.png differ
diff --git a/2-ui/3-event-details/5-keyboard-events/german-layout@2x.png b/2-ui/3-event-details/5-keyboard-events/german-layout@2x.png
new file mode 100644
index 000000000..30f6e0d13
Binary files /dev/null and b/2-ui/3-event-details/5-keyboard-events/german-layout@2x.png differ
diff --git a/2-ui/3-event-details/5-keyboard-events/us-layout.png b/2-ui/3-event-details/5-keyboard-events/us-layout.png
new file mode 100644
index 000000000..a42dd80fe
Binary files /dev/null and b/2-ui/3-event-details/5-keyboard-events/us-layout.png differ
diff --git a/2-ui/3-event-details/5-keyboard-events/us-layout@2x.png b/2-ui/3-event-details/5-keyboard-events/us-layout@2x.png
new file mode 100644
index 000000000..fd583b74d
Binary files /dev/null and b/2-ui/3-event-details/5-keyboard-events/us-layout@2x.png differ
diff --git a/2-ui/4-forms-controls/2-focus-blur/3-editable-div/solution.view/my.css b/2-ui/4-forms-controls/2-focus-blur/3-editable-div/solution.view/my.css
index 67905e6d6..bf3d4ff6a 100644
--- a/2-ui/4-forms-controls/2-focus-blur/3-editable-div/solution.view/my.css
+++ b/2-ui/4-forms-controls/2-focus-blur/3-editable-div/solution.view/my.css
@@ -20,6 +20,6 @@
 }
 
 .edit:focus {
-  outline: none;
   /* remove focus border in Safari */
+  outline: none;
 }
diff --git a/2-ui/4-forms-controls/2-focus-blur/3-editable-div/source.view/my.css b/2-ui/4-forms-controls/2-focus-blur/3-editable-div/source.view/my.css
index 67905e6d6..bf3d4ff6a 100644
--- a/2-ui/4-forms-controls/2-focus-blur/3-editable-div/source.view/my.css
+++ b/2-ui/4-forms-controls/2-focus-blur/3-editable-div/source.view/my.css
@@ -20,6 +20,6 @@
 }
 
 .edit:focus {
-  outline: none;
   /* remove focus border in Safari */
+  outline: none;
 }
diff --git a/2-ui/4-forms-controls/2-focus-blur/4-edit-td-click/solution.view/my.css b/2-ui/4-forms-controls/2-focus-blur/4-edit-td-click/solution.view/my.css
index d7f2a4424..8d0c3b4ec 100644
--- a/2-ui/4-forms-controls/2-focus-blur/4-edit-td-click/solution.view/my.css
+++ b/2-ui/4-forms-controls/2-focus-blur/4-edit-td-click/solution.view/my.css
@@ -3,14 +3,15 @@
   margin: 0;
   padding: 0;
   display: block;
-  resize: none;
+  
   /* remove resizing handle in Firefox */
+  resize: none;
   
-  outline: none;
   /* remove outline on focus in Chrome */
+  outline: none;
   
-  overflow: auto;
   /* remove scrollbar in IE */
+  overflow: auto;
 }
 
 .edit-controls {
diff --git a/2-ui/4-forms-controls/2-focus-blur/5-keyboard-mouse/solution.md b/2-ui/4-forms-controls/2-focus-blur/5-keyboard-mouse/solution.md
index 2c5c73cd3..4d1682176 100644
--- a/2-ui/4-forms-controls/2-focus-blur/5-keyboard-mouse/solution.md
+++ b/2-ui/4-forms-controls/2-focus-blur/5-keyboard-mouse/solution.md
@@ -1,5 +1,5 @@
 
-We can use `mouse.onclick` to handle the click and make the mouse "moveable" with `position:fixed`, then then `mouse.onkeydown` to handle arrow keys.
+We can use `mouse.onclick` to handle the click and make the mouse "moveable" with `position:fixed`, then `mouse.onkeydown` to handle arrow keys.
 
 The only pitfall is that `keydown` only triggers on elements with focus. So we need to add `tabindex` to the element.  As we're forbidden to change HTML, we can use `mouse.tabIndex` property for that.
 
diff --git a/2-ui/4-forms-controls/2-focus-blur/article.md b/2-ui/4-forms-controls/2-focus-blur/article.md
index 1a880ce47..695b69c97 100644
--- a/2-ui/4-forms-controls/2-focus-blur/article.md
+++ b/2-ui/4-forms-controls/2-focus-blur/article.md
@@ -2,13 +2,13 @@
 
 An element receives a focus when the user either clicks on it or uses the `key:Tab` key on the keyboard. There's also an `autofocus` HTML attribute that puts the focus into an element by default when a page loads and other means of getting a focus.
 
-Focusing generally means: "prepare to accept the data here", so that's the moment when we can run the code to initialize or load something.
+Focusing on an element generally means: "prepare to accept the data here", so that's the moment when we can run the code to initialize the required functionality.
 
 The moment of losing the focus ("blur") can be even more important. That's when a user clicks somewhere else or presses `key:Tab` to go to the next form field, or there are other means as well.
 
 Losing the focus generally means: "the data has been entered", so we can run the code to check it or even to save it to the server and so on.
 
-There are important peculiarities when working with focus events. We'll do the best to cover them here.
+There are important peculiarities when working with focus events. We'll do the best to cover them further on.
 
 ## Events focus/blur
 
@@ -203,7 +203,6 @@ So here's another working variant:
 
 <script>
 *!*
-  // put the handler on capturing phase (last argument true)
   form.addEventListener("focusin", () => form.classList.add('focused'));
   form.addEventListener("focusout", () => form.classList.remove('focused'));
 */!*
diff --git a/2-ui/5-loading/01-onload-ondomcontentloaded/article.md b/2-ui/5-loading/01-onload-ondomcontentloaded/article.md
index 2d60aa1d3..34fcd7a3b 100644
--- a/2-ui/5-loading/01-onload-ondomcontentloaded/article.md
+++ b/2-ui/5-loading/01-onload-ondomcontentloaded/article.md
@@ -3,13 +3,13 @@
 The lifecycle of an HTML page has three important events:
 
 - `DOMContentLoaded` -- the browser fully loaded HTML, and the DOM tree is built, but external resources like pictures `<img>` and stylesheets may be not yet loaded.  
-- `load` -- the browser loaded all resources (images, styles etc).
-- `beforeunload/unload` -- when the user is leaving the page.
+- `load` -- not only HTML is loaded, but also all the external resources: images, styles etc.
+- `beforeunload/unload` -- the user is leaving the page.
 
 Each event may be useful:
 
 - `DOMContentLoaded` event -- DOM is ready, so the handler can lookup DOM nodes, initialize the interface.
-- `load` event -- additional resources are loaded, we can get image sizes (if not specified in HTML/CSS) etc.
+- `load` event -- external resources are loaded, so styles are applied, image sizes are known etc.
 - `beforeunload` event -- the user is leaving: we can check if the user saved the changes and ask them whether they really want to leave.
 - `unload` -- the user almost left, but we still can initiate some operations, such as sending out statistics.
 
@@ -60,7 +60,7 @@ So DOMContentLoaded definitely happens after such scripts:
 ```html run
 <script>
   document.addEventListener("DOMContentLoaded", () => {
-    console.log("DOM ready!");
+    alert("DOM ready!");
   });
 </script>
 
diff --git a/2-ui/5-loading/02-script-async-defer/article.md b/2-ui/5-loading/02-script-async-defer/article.md
index f5c3faeb1..b3e4892b3 100644
--- a/2-ui/5-loading/02-script-async-defer/article.md
+++ b/2-ui/5-loading/02-script-async-defer/article.md
@@ -29,11 +29,11 @@ There are some workarounds to that. For instance, we can put a script at the bot
 </body>
 ```
 
-But this solution is far from perfect. For example, the browser actually notices the script (and can start downloading it) only after it downloaded the full HTML document. For long HTML documents, that may be a noticeable delay.
+But this solution is far from perfect. For example, the browser notices the script (and can start downloading it) only after it downloaded the full HTML document. For long HTML documents, that may be a noticeable delay.
 
-Such things are invisible for people using very fast connections, but many people in the world still have slower internet speeds and far-from-perfect mobile connectivity.
+Such things are invisible for people using very fast connections, but many people in the world still have slower internet speeds and use far-from-perfect mobile internet.
 
-Luckily, there are two `<script>` attributes that solve the problem for us: `defer` and `async`
+Luckily, there are two `<script>` attributes that solve the problem for us: `defer` and `async`.
 
 ## defer
 
@@ -75,24 +75,24 @@ Deferred scripts keep their relative order, just like regular scripts.
 So, if we have a long script first, and then a smaller one, then the latter one waits.
 
 ```html
-<script async src="https://javascript.info/article/script-async-defer/long.js"></script>
-<script async src="https://javascript.info/article/script-async-defer/small.js"></script>
+<script defer src="https://javascript.info/article/script-async-defer/long.js"></script>
+<script defer src="https://javascript.info/article/script-async-defer/small.js"></script>
 ```
 
 ```smart header="The small script downloads first, runs second"
 Browsers scan the page for scripts and download them in parallel, to improve performance. So in the example above both scripts download in parallel. The `small.js` probably makes it first.
 
-But the specification requres scripts to execute in the document order, so it waits for `long.js` to execute.
+But the specification requires scripts to execute in the document order, so it waits for `long.js` to execute.
 ```
 
 ```smart header="The `defer` attribute is only for external scripts"
-The `defer` attribute is ignored if the script has no `src`.
+The `defer` attribute is ignored if the `<script>` tag has no `src`.
 ```
 
 
 ## async
 
-The `async` attribute means that a script is completely independant:
+The `async` attribute means that a script is completely independent:
 
 - The page doesn't wait for async scripts, the contents is processed and displayed.
 - `DOMContentLoaded` and async scripts don't wait each other:
@@ -120,16 +120,17 @@ So, if we have several `async` scripts, they may execute in any order. Whatever
 2. `DOMContentLoaded` may happen both before and after `async`, no guarantees here.
 3. Async scripts don't wait for each other. A smaller script `small.js` goes second, but probably loads before `long.js`, so runs first. That's called a "load-first" order.
 
-Async scripts are great when we integrate an independant third-party script into the page: counters, ads and so on.
+Async scripts are great when we integrate an independent third-party script into the page: counters, ads and so on, as they don't depend on our scripts, and our scripts shouldn't wait for them:
 
 ```html
+<!-- Google Analytics is usually added like this -->
 <script async src="https://google-analytics.com/analytics.js"></script>
 ```
 
 
 ## Dynamic scripts
 
-We can also create a script dynamically using JavaScript:
+We can also add a script dynamically using JavaScript:
 
 ```js run
 let script = document.createElement('script');
@@ -145,7 +146,7 @@ That is:
 - They don't wait for anything, nothing waits for them.
 - The script that loads first -- runs first ("load-first" order).
 
-We can change the load-first order into the document order by explicitly setting `async` to `false`:
+We can change the load-first order into the document order (just like regular scripts) by explicitly setting `async` property to `false`:
 
 ```js run
 let script = document.createElement('script');
@@ -191,7 +192,4 @@ Please note that if you're using `defer`, then the page is visible before the sc
 
 So, buttons should be disabled by CSS or by other means, to let the user
 
-In practice, `defer` is used for scripts that need DOM and/or their relative execution order is important.
-
-
-So `async` is used for independent scripts, like counters or ads, that don't need to access page content. And their relative execution order does not matter.
+In practice, `defer` is used for scripts that need the whole DOM and/or their relative execution order is important. And  `async` is used for independent scripts, like counters or ads. And their relative execution order does not matter.
diff --git a/2-ui/5-loading/02-script-async-defer/window-onbeforeunload.view/index.html b/2-ui/5-loading/02-script-async-defer/window-onbeforeunload.view/index.html
deleted file mode 100644
index eacfda1f7..000000000
--- a/2-ui/5-loading/02-script-async-defer/window-onbeforeunload.view/index.html
+++ /dev/null
@@ -1,19 +0,0 @@
-<!DOCTYPE html>
-<html>
-<head>
-  <meta charset="utf-8">
-</head>
-<body>
-  <script>
-    function setHandler() {
-      window.onbeforeunload = function() {
-        return "There are unsaved changes. Leave now?";
-      };
-    }
-  </script>
-
-  <button onclick="setHandler()">Set window.onbeforeunload</button>
-
-  <a href="http://example.com">Leave for EXAMPLE.COM</a>
-</body>
-</html>
diff --git a/2-ui/5-loading/03-onload-onerror/article.md b/2-ui/5-loading/03-onload-onerror/article.md
index e915dedb6..56b8165b6 100644
--- a/2-ui/5-loading/03-onload-onerror/article.md
+++ b/2-ui/5-loading/03-onload-onerror/article.md
@@ -92,7 +92,7 @@ img.onload = function() {
 };
 
 img.onerror = function() {
-  alert("Error occured while loading image");
+  alert("Error occurred while loading image");
 };
 ```
 
@@ -155,7 +155,7 @@ Script error.
 , 0:0
 ```
 
-Details may vary depeding on the browser, but the idea is same: any information about the internals of a script is hidden. Exactly because it's from another domain.
+Details may vary depending on the browser, but the idea is same: any information about the internals of a script is hidden. Exactly because it's from another domain.
 
 Why do we need the details?
 
diff --git a/3-frames-and-windows/01-popup-windows/article.md b/3-frames-and-windows/01-popup-windows/article.md
index 57c0c50d3..52d6768ab 100644
--- a/3-frames-and-windows/01-popup-windows/article.md
+++ b/3-frames-and-windows/01-popup-windows/article.md
@@ -13,7 +13,7 @@ window.open('https://javascript.info/')
 
 Popups exist from really ancient times. The initial idea was to show another content without closing the main window. As of now, there are other ways to do that: JavaScript is able to send requests for server, so popups are rarely used. But sometimes they are still handy.
 
-In the past evil sites abused popups a lot. A bad page could open tons of popup windows with ads. So now most browsers try to block popups and protect the user.
+In the past, evil sites abused popups a lot. A bad page could open tons of popup windows with ads. So now most browsers try to block popups and protect the user.
 
 **Most browsers block popups if they are called outside of user-triggered event handlers like `onclick`.**
 
@@ -52,15 +52,11 @@ The difference is that Firefox treats a timeout of 2000ms or less are acceptable
 
 ## Modern usage
 
-As of now, we have many methods to load and show data on-page with JavaScript. But there are still situations when a popup works best.
+As of now, we have many methods to load and show data on-page with JavaScript. But there are still situations when a popup works good, because:
 
-For instance, many shops use online chats for consulting people. A visitor clicks on the button, it runs `window.open` and opens the popup with the chat.
-
-Why a popup is good here, why not in-page?
-
-1. A popup is a separate window with its own independent JavaScript environment. So a chat service doesn't need to integrate with scripts of the main shop site.
-2. A popup is very simple to attach to a site, little to no overhead. It's only a small button, without additional scripts.
-3. A popup may persist even if the user left the page. For example, a consult advices the user to visit the page of a new "Super-Cooler" goodie. The user goes there in the main window without leaving the chat.
+1. A popup is a separate window with its own independent JavaScript environment. So opening a popup with a third-party non-trusted site is safe.
+2. It's very easy to open a popup, little to no overhead. 
+3. A popup may persist even if the user left the page. In also can navigate (change URL) in the opener window.
 
 ## window.open
 
@@ -118,7 +114,7 @@ Most browsers show the example above as required.
 Rules for omitted settings:
 
 - If there is no 3rd argument in the `open` call, or it is empty, then the default window parameters are used.
-- If there is a string of params, but some yes/no features are omitted, then the omitted features are disabled, if the browser allows that. So if you specify params, make sure you explicitly set all required features to yes.
+- If there is a string of params, but some `yes/no` features are omitted, then the omitted features assumed to have `no` value. So if you specify params, make sure you explicitly set all required features to yes.
 - If there is no `left/top` in params, then the browser tries to open a new window near the last opened window.
 - If there is no `width/height`, then the new window will be the same size as the last opened.
 
diff --git a/4-binary/01-arraybuffer-binary-arrays/article.md b/4-binary/01-arraybuffer-binary-arrays/article.md
index d0bb488db..de4e719b2 100644
--- a/4-binary/01-arraybuffer-binary-arrays/article.md
+++ b/4-binary/01-arraybuffer-binary-arrays/article.md
@@ -9,7 +9,7 @@ Although, there's a bit of confusion, because there are many classes. To name a
 
 Binary data in JavaScript is implemented in a non-standard way, compared to other languages. But when we sort things out, everything becomes fairly simple.
 
-**The basic binary object is `ArrayBuffer` -- a reference to a fixed-length contiguos memory area.**
+**The basic binary object is `ArrayBuffer` -- a reference to a fixed-length contiguous memory area.**
 
 We create it like this:
 ```js run
@@ -209,7 +209,7 @@ These methods allow us to copy typed arrays, mix them, create new arrays from ex
 [DataView](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView) is a special super-flexible "untyped" view over `ArrayBuffer`. It allows to access the data on any offset in any format.
 
 - For typed arrays, the constructor dictates what the format is. The whole array is supposed to be uniform. The i-th number is `arr[i]`.
-- With `DataView` we access the data with methods like `.getUint8(i)` or `.gteUint16(i)`. We choose the format at method call time instead of the construction time.
+- With `DataView` we access the data with methods like `.getUint8(i)` or `.getUint16(i)`. We choose the format at method call time instead of the construction time.
 
 The syntax:
 
@@ -249,7 +249,7 @@ dataView.setUint32(0, 0); // set 4-byte number to zero
 To do almost any operation on `ArrayBuffer`, we need a view.
 
 - It can be a `TypedArray`:
-    - `Uint8Array`, `Uint16Array`, `Uint32Array` -- for integer numbers of 8, 16 and 32 bits.
+    - `Uint8Array`, `Uint16Array`, `Uint32Array` -- for unsigned integers of 8, 16, and 32 bits.
     - `Uint8ClampedArray` -- for 8-bit integers, "clamps" them on assignment.
     - `Int8Array`, `Int16Array`, `Int32Array` -- for signed integer numbers (can be negative).
     - `Float32Array`, `Float64Array` -- for signed floating-point numbers of 32 and 64 bits.
@@ -261,7 +261,7 @@ There are also two additional terms:
 - `ArrayBufferView` is an umbrella term for all these kinds of views.
 - `BufferSource` is an umbrella term for `ArrayBuffer` or `ArrayBufferView`.
 
-These are used in descriptions of methods that operate on binary data. `BufferSource` is one of the most common teerms, as it means "any kind of binary data" -- an `ArrayBuffer` or a view over it. 
+These are used in descriptions of methods that operate on binary data. `BufferSource` is one of the most common terms, as it means "any kind of binary data" -- an `ArrayBuffer` or a view over it. 
 
 
 Here's a cheatsheet:
diff --git a/4-binary/03-blob/article.md b/4-binary/03-blob/article.md
index d75973ea7..d0d176784 100644
--- a/4-binary/03-blob/article.md
+++ b/4-binary/03-blob/article.md
@@ -2,14 +2,12 @@
 
 `ArrayBuffer` and views are a part of ECMA standard, a part of JavaScript.
 
-In the browser, there are additional higher-level objects, described in [File API](https://www.w3.org/TR/FileAPI/).
+In the browser, there are additional higher-level objects, described in [File API](https://www.w3.org/TR/FileAPI/), in particular `Blob`.
 
 `Blob` consists of an optional string `type` (a MIME-type usually), plus `blobParts` -- a sequence of other `Blob` objects, strings and `BufferSources`.
 
 ![](blob.png)
 
-Thanks to `type`, we can download/upload blobs, and it naturally becomes `Content-Type` in network requests.
-
 The constructor syntax is:
 
 ```js
@@ -59,7 +57,10 @@ This behavior is similar to JavaScript strings: we can't change a character in a
 
 A Blob can be easily used as an URL for `<a>`, `<img>` or other tags, to show its contents.
 
-Let's start with a simple example. By clicking on a link you download a dynamically-generated blob with `hello world` contents as a file:
+Thanks to `type`, we can allso download/upload blobs, and it naturally becomes `Content-Type` in network requests.
+
+Let's start with a simple example. By\
+ clicking on a link you download a dynamically-generated blob with `hello world` contents as a file:
 
 ```html run
 <!-- download attribute forces the browser to download instead of navigating -->
@@ -72,9 +73,9 @@ link.href = URL.createObjectURL(blob);
 </script>
 ```
 
-We can also create a link dynamically in JavaScript and simulate a click by `link.click()`, then download starts authomatically.
+We can also create a link dynamically in JavaScript and simulate a click by `link.click()`, then download starts automatically.
 
-Here's the similar "on the fly" blob creation and download code, but without HTML:
+Here's the similar code that causes user to download the dynamicallly created Blob, without any HTML:
 
 ```js run
 let link = document.createElement('a');
@@ -89,9 +90,9 @@ link.click();
 URL.revokeObjectURL(link.href);
 ```
 
-**`URL.createObjectURL` takes a blob and creates an unique URL for it, in the form `blob:<origin>/<uuid>`.**
+`URL.createObjectURL` takes a blob and creates an unique URL for it, in the form `blob:<origin>/<uuid>`.
 
-That's what the generated url looks like:
+That's what the value of `link.href` looks like:
 
 ```
 blob:https://javascript.info/1e67e00e-860d-40a5-89ae-6ab0cbee6273
@@ -99,13 +100,15 @@ blob:https://javascript.info/1e67e00e-860d-40a5-89ae-6ab0cbee6273
 
 The browser for each url generated by `URL.createObjectURL` stores an the url -> blob mapping internally. So such urls are short, but allow to access the blob.
 
-A generated url is only valid while the current document is open. And it allows to reference the blob in `<img>`, `<a>`, any other object that expects an url.
+A generated url (and hence the link with it) is only valid within the current document, while it's open. And it allows to reference the blob in `<img>`, `<a>`, basically any other object that expects an url.
 
 There's a side-effect though. While there's an mapping for a blob, the blob itself resides in the memory. The browser can't free it.
 
-The mapping is automatically cleared on document unload, so blobs are freed then. But if an app is long-living, then that doesn't happen soon. So if we create an URL, that blob will hang in memory, even if not needed any more.
+The mapping is automatically cleared on document unload, so blobs are freed then. But if an app is long-living, then that doesn't happen soon.
+
+**So if we create an URL, that blob will hang in memory, even if not needed any more.**
 
-**`URL.revokeObjectURL(url)` removes the reference from the internal mapping, thus allowing the blob to be deleted (if there are no other references), and the memory to be freed.**
+`URL.revokeObjectURL(url)` removes the reference from the internal mapping, thus allowing the blob to be deleted (if there are no other references), and the memory to be freed.
 
 In the last example, we intend the blob to be used only once, for instant downloading, so we call `URL.revokeObjectURL(link.href)` immediately.
 
diff --git a/4-binary/04-file/article.md b/4-binary/04-file/article.md
index e9a01b1b4..281ca211f 100644
--- a/4-binary/04-file/article.md
+++ b/4-binary/04-file/article.md
@@ -1,6 +1,6 @@
 # File and FileReader
 
-A [File](https://www.w3.org/TR/FileAPI/#dfn-file) object inhereits from `Blob`, but is extended with filesystem-related capabilities.
+A [File](https://www.w3.org/TR/FileAPI/#dfn-file) object inherits from `Blob` and is extended with filesystem-related capabilities.
 
 There are two ways to obtain it.
 
@@ -38,9 +38,9 @@ The input may select multiple files, so `input.files` is an array-like object wi
 
 ## FileReader
 
-[FileReader](https://www.w3.org/TR/FileAPI/#dfn-filereader) is an object with the sole purpose of reading from `Blob` (and hence `File` too) objects.
+[FileReader](https://www.w3.org/TR/FileAPI/#dfn-filereader) is an object with the sole purpose of reading data from `Blob` (and hence `File` too) objects.
 
-It's event based, as reading from disk may take time.
+It delivers the data using events, as reading from disk may take time.
 
 The constructor:
 
@@ -60,7 +60,7 @@ As the reading proceeds, there are events:
 - `progress` -- occurs during reading.
 - `load` -- no errors, reading complete.
 - `abort` -- `abort()` called.
-- `error` -- error has occured.
+- `error` -- error has occurred.
 - `loadend` -- reading finished with either success or failure.
 
 When the reading is finished, we can access the result as:
@@ -109,12 +109,12 @@ For Web Workers, there also exists a synchronous variant of `FileReader`, called
 
 Its reading methods `read*` do not generate events, but rather return a result, as regular functions do.
 
-That's only inside a Web Worker though, because delays and hang-ups in Web Workers are less important, they do not affect the page.
+That's only inside a Web Worker though, because delays in synchronous calls, that are possible while reading from files, in Web Workers are less important. They do not affect the page.
 ```
 
 ## Summary
 
-`File` object inherit from `Blob`.
+`File` objects inherit from `Blob`.
 
 In addition to `Blob` methods and properties, `File` objects also have `fileName` and `lastModified` properties, plus the internal ability to read from filesystem. We usually get `File` objects from user input, like `<input>` or drag'n'drop.
 
diff --git a/5-network/02-fetch-progress/article.md b/5-network/02-fetch-progress/article.md
index e7e945f66..5c022eb3f 100644
--- a/5-network/02-fetch-progress/article.md
+++ b/5-network/02-fetch-progress/article.md
@@ -1,7 +1,7 @@
 
 # Fetch: Download progress
 
-Fetch allows to track download progress, but not upload progress.
+The `fetch` method allows to track download progress.
 
 Please note: there's currently no way for fetch to track upload progress. For that purpose, please use [XMLHttpRequest](info:xmlhttprequest).
 
diff --git a/5-network/04-fetch-crossorigin/article.md b/5-network/04-fetch-crossorigin/article.md
index e1b669e0e..4d659a80a 100644
--- a/5-network/04-fetch-crossorigin/article.md
+++ b/5-network/04-fetch-crossorigin/article.md
@@ -198,7 +198,7 @@ A preflight request uses method `OPTIONS` and has no body.
 
 If the server agrees to serve the requests, then it should respond with status 200, without body.
 
-- The response header `Access-Control-Allow-Method` must have the allowed method.
+- The response header `Access-Control-Allow-Methods` must have the allowed method.
 - The response header `Access-Control-Allow-Headers` must have a list of allowed headers.
 - Additionally, the header `Access-Control-Max-Age` may specify a number of seconds to cache the permissions. So the browser won't have to send a preflight for subsequent requests that satisfy given permissions.
 
@@ -243,7 +243,7 @@ Access-Control-Request-Headers: Content-Type,API-Key
 ### Step 2 (preflight response)
 
 The server should respond with status 200 and headers:
-- `Access-Control-Allow-Method: PATCH`
+- `Access-Control-Allow-Methods: PATCH`
 - `Access-Control-Allow-Headers: Content-Type,API-Key`.
 
 That would allow future communication, otherwise an error is triggered.
@@ -277,7 +277,7 @@ Origin: https://javascript.info
 
 ### Step 4 (actual response)
 
-The server should not forget to add `Accept-Control-Allow-Origin` to the response. A successful preflight does not relieve from that:
+The server should not forget to add `Access-Control-Allow-Origin` to the response. A successful preflight does not relieve from that:
 
 ```
 Access-Control-Allow-Origin: https://javascript.info
@@ -348,7 +348,7 @@ So, practical difference is that simple requests are sent right away, with `Orig
     - `Access-Control-Allow-Origin` to `Origin`
     - `Access-Control-Allow-Credentials` to `true`
 
-Additionally, if JavaScript wants no access non-simple response headers:
+Additionally, if JavaScript wants to access non-simple response headers:
 - `Cache-Control`
 - `Content-Language`
 - `Content-Type`
@@ -364,7 +364,7 @@ Additionally, if JavaScript wants no access non-simple response headers:
     - `Access-Control-Request-Method` has requested method.
     - `Access-Control-Request-Headers` lists non-simple requested headers
 - ← The server should respond with status 200 and headers:
-    - `Access-Control-Allow-Method` with a list of allowed methods,
+    - `Access-Control-Allow-Methods` with a list of allowed methods,
     - `Access-Control-Allow-Headers` with a list of allowed headers,
     - `Access-Control-Max-Age` with a number of seconds to cache permissions.
 - Then the actual request is sent, the previous "simple" scheme is applied.
diff --git a/5-network/06-url/article.md b/5-network/06-url/article.md
index 61c4f9414..4615a4e55 100644
--- a/5-network/06-url/article.md
+++ b/5-network/06-url/article.md
@@ -33,7 +33,7 @@ Here's the cheatsheet:
 - `href` is the full url, same as `url.toString()`
 - `protocol` ends with the colon character `:`
 - `search` starts with the question mark `?`
-- `hash` ends with the hash character `#`
+- `hash` starts with the hash character `#`
 - there are also `user` and `password` properties if HTTP authentication is present.
 
 We can also use `URL` to create relative urls, using the second argument:
@@ -60,7 +60,7 @@ Let's say we want to create an url with given search params, for instance, `http
 
 They must be correctly encoded.
 
-In very old browsers, before `URL` apparead, we'd use built-in functions `encodeURIComponent/decodeURIComponent`.
+In very old browsers, before `URL` appeared, we'd use built-in functions `encodeURIComponent/decodeURIComponent`.
 
 Now, there's no need: `url.searchParams` is an object of type [URLSearchParams](https://url.spec.whatwg.org/#urlsearchparams).
 
diff --git a/5-network/07-xmlhttprequest/article.md b/5-network/07-xmlhttprequest/article.md
index bda4bd1b7..c6b3d6293 100644
--- a/5-network/07-xmlhttprequest/article.md
+++ b/5-network/07-xmlhttprequest/article.md
@@ -12,7 +12,7 @@ In modern web-development `XMLHttpRequest` may be used for three reasons:
 2. We need to support old browsers, and don't want polyfills (e.g. to keep scripts tiny).
 3. We need something that `fetch` can't do yet, e.g. to track upload progress.
 
-Does that sound familiar? If yes, then all right, go on with `XMLHttpRequest`. Otherwise, please head on to fetch (coming soon).
+Does that sound familiar? If yes, then all right, go on with `XMLHttpRequest`. Otherwise, please head on to <info:fetch-basics>.
 
 ## Basic flow
 
@@ -143,7 +143,7 @@ We can use `xhr.responseType` property to set the response format:
 
 - `""` (default) -- get as string,
 - `"text"` -- get as string,
-- `"arraybuffer"` -- get as `ArrayBuffer` (for binary data, see chapter <info:arraybuffer-and-views>),
+- `"arraybuffer"` -- get as `ArrayBuffer` (for binary data, see chapter <info:arraybuffer-binary-arrays>),
 - `"blob"` -- get as `Blob` (for binary data, see chapter <info:blob>),
 - `"document"` -- get as XML document (can use XPath and other XML methods),
 - `"json"` -- get as JSON (parsed automatically).
@@ -261,7 +261,7 @@ There are 3 methods for HTTP-headers:
     ```
 
     ````warn header="Can't remove a header"
-    Another peciliarity of `XMLHttpRequest` is that one can't undo `setRequestHeader`.
+    Another peculiarity of `XMLHttpRequest` is that one can't undo `setRequestHeader`.
 
     Once the header is set, it's set. Additional calls add information to the header, don't overwrite it.
 
@@ -495,7 +495,7 @@ There are actually more events, the [modern specification](http://www.w3.org/TR/
 - `loadstart` -- the request has started.
 - `progress` -- a data packet of the response has arrived, the whole response body at the moment is in `responseText`.
 - `abort` -- the request was canceled by the call `xhr.abort()`.
-- `error` -- connection error has occured, e.g. wrong domain name. Doesn't happen for HTTP-errors like 404.
+- `error` -- connection error has occurred, e.g. wrong domain name. Doesn't happen for HTTP-errors like 404.
 - `load` -- the request has finished successfully.
 - `timeout` -- the request was canceled due to timeout (only happens if it was set).
 - `loadend` -- the request has finished (succeffully or not).
diff --git a/5-network/08-websocket/article.md b/5-network/08-websocket/article.md
index f7bd1fa2c..2b5faf486 100644
--- a/5-network/08-websocket/article.md
+++ b/5-network/08-websocket/article.md
@@ -130,7 +130,7 @@ For instance:
 let socket = new WebSocket("wss://javascript.info/chat", ["soap", "wamp"]);
 ```
 
-The server should respond with a list of protocls and extensions that it agrees to use.
+The server should respond with a list of protocols and extensions that it agrees to use.
 
 For example, the request:
 
@@ -312,7 +312,7 @@ socket.onmessage = function(event) {
 }
 ```
 
-Server-side code is a little bit beyound our scope here. We're using browser WebSocket API, a server may have another library.
+Server-side code is a little bit beyond our scope here. We're using browser WebSocket API, a server may have another library.
 
 Still it can also be pretty simple. We'll use Node.js with <https://github.com/websockets/ws> module for websockets.
 
diff --git a/6-data-storage/02-localstorage/article.md b/6-data-storage/02-localstorage/article.md
index 41a895b05..ec3c0e647 100644
--- a/6-data-storage/02-localstorage/article.md
+++ b/6-data-storage/02-localstorage/article.md
@@ -7,7 +7,7 @@ What's interesting about them is that the data survives a page refresh (for `ses
 We already have cookies. Why additional objects?
 
 - Unlike cookies, web storage objects are not sent to server with each request. Because of that, we can store much more. Most browsers allow at least 2 megabytes of data (or more) and have settings to configure that.
-- The server can't manipulate storage objects via HTTP headers, everything's done in JavaScript.
+- Also unlike cookies, the server can't manipulate storage objects via HTTP headers. Everything's done in JavaScript.
 - The storage is bound to the origin (domain/protocol/port triplet). That is, different protocols or subdomains infer different storage objects, they can't access data from each other.
 
 Both storage objects provide same methods and properties:
@@ -19,6 +19,8 @@ Both storage objects provide same methods and properties:
 - `key(index)` -- get the key on a given position.
 - `length` -- the number of stored items.
 
+As you can see, it's like a `Map` colection (`setItem/getItem/removeItem`), but also keeps elements order and allows to access by index with `key(index)`.
+
 Let's see how it works.
 
 ## localStorage demo
@@ -71,11 +73,11 @@ That's allowed for historical reasons, and mostly works, but generally not recom
 
 ## Looping over keys
 
-Methods provide get/set/remove functionality. But how to get all the keys?
+As we've seen, the methods provide get/set/remove functionality. But how to get all saved values or keys?
 
 Unfortunately, storage objects are not iterable.
 
-One way is to use "array-like" iteration:
+One way is to loop over them as over an array:
 
 ```js run
 for(let i=0; i<localStorage.length; i++) {
@@ -84,9 +86,9 @@ for(let i=0; i<localStorage.length; i++) {
 }
 ```
 
-Another way is to use object-specific `for key in localStorage` loop.
+Another way is to use `for key in localStorage` loop, just as we do with regular objects.
 
-That iterates over keys, but also outputs few built-in fields that we don't need:
+It iterates over keys, but also outputs few built-in fields that we don't need:
 
 ```js run
 // bad try
@@ -122,7 +124,7 @@ The latter works, because `Object.keys` only returns the keys that belong to the
 
 Please note that both key and value must be strings.
 
-If we any other type, like a number, or an object, it gets converted to string automatically:
+If were any other type, like a number, or an object, it gets converted to string automatically:
 
 ```js run
 sessionStorage.user = {name: "John"};
@@ -180,7 +182,7 @@ That's exactly because `sessionStorage` is bound not only to the origin, but als
 
 When the data gets updated in `localStorage` or `sessionStorage`, [storage](https://www.w3.org/TR/webstorage/#the-storage-event) event triggers, with properties:
 
-- `key` – the key that was changed (null if `.clear()` is called).
+- `key` – the key that was changed (`null` if `.clear()` is called).
 - `oldValue` – the old value (`null` if the key is newly added).
 - `newValue` – the new value (`null` if the key is removed).
 - `url` – the url of the document where the update happened.
diff --git a/7-animation/1-bezier-curve/article.md b/7-animation/1-bezier-curve/article.md
index 6166f25c1..4a8065143 100644
--- a/7-animation/1-bezier-curve/article.md
+++ b/7-animation/1-bezier-curve/article.md
@@ -2,7 +2,7 @@
 
 Bezier curves are used in computer graphics to draw shapes, for CSS animation and in many other places.
 
-They are actually a very simple thing, worth to study once and then feel comfortable in the world of vector graphics and advanced animations.
+They are a very simple thing, worth to study once and then feel comfortable in the world of vector graphics and advanced animations.
 
 ## Control points
 
@@ -130,14 +130,14 @@ A non-smooth Bezier curve (yeah, that's possible too):
 [iframe src="demo.svg?p=0,0,1,1,0,1,1,0&animate=1" height=370]
 
 ```online
-If there's anything unclear in the algorithm description, then live examples above show how
+If there's something unclear in the algorithm description, please look at the live examples above to see how
 the curve is built.
 ```
 
 As the algorithm is recursive, we can build Bezier curves of any order, that is: using 5, 6 or more control points. But in practice many points are less useful. Usually we take 2-3 points, and for complex lines glue several curves together. That's simpler to develop and calculate.
 
 ```smart header="How to draw a curve *through* given points?"
-We use control points for a Bezier curve. As we can see, they are not on the curve, except the first and the last ones.
+To specify a Bezier curve, control points are used. As we can see, they are not on the curve, except the first and the last ones.
 
 Sometimes we have another task: to draw a curve *through several points*, so that all of them are on a single smooth curve. That task is called  [interpolation](https://en.wikipedia.org/wiki/Interpolation), and here we don't cover it.
 
@@ -186,12 +186,12 @@ Bezier curves are defined by their control points.
 
 We saw two definitions of Bezier curves:
 
-1. Using a mathematical formulas.
-2. Using a drawing process: De Casteljau's algorithm
+1. Using a drawing process: De Casteljau's algorithm.
+2. Using a mathematical formulas.
 
 Good properties of Bezier curves:
 
-- We can draw smooth lines with a mouse by moving around control points.
+- We can draw smooth lines with a mouse by moving control points.
 - Complex shapes can be made of several Bezier curves.
 
 Usage:
diff --git a/7-animation/3-js-animation/1-animate-ball/solution.md b/7-animation/3-js-animation/1-animate-ball/solution.md
index 3a9b8564f..5d3f08eef 100644
--- a/7-animation/3-js-animation/1-animate-ball/solution.md
+++ b/7-animation/3-js-animation/1-animate-ball/solution.md
@@ -1,10 +1,8 @@
 To bounce we can use CSS property `top` and `position:absolute` for the ball inside the field with `position:relative`.
 
-The bottom coordinate of the field is `field.clientHeight`. But the `top` property gives coordinates for the top of the ball, the edge position is `field.clientHeight - ball.clientHeight`.
+The bottom coordinate of the field is `field.clientHeight`. The CSS `top` property refers to the upper edge of the ball. So it should go from `0` till `field.clientHeight - ball.clientHeight`, that's the final lowest position of the upper edge of the ball.
 
-So we animate the `top` from `0` to `field.clientHeight - ball.clientHeight`.
-
-Now to get the "bouncing" effect we can use the timing function `bounce` in `easeOut` mode.
+To to get the "bouncing" effect we can use the timing function `bounce` in `easeOut` mode.
 
 Here's the final code for the animation:
 
diff --git a/7-animation/3-js-animation/article.md b/7-animation/3-js-animation/article.md
index 0975ebff5..d3e12fcaf 100644
--- a/7-animation/3-js-animation/article.md
+++ b/7-animation/3-js-animation/article.md
@@ -55,7 +55,7 @@ Let's imagine we have several animations running simultaneously.
 
 If we run them separately, then even though each one has `setInterval(..., 20)`, then the browser would have to repaint much more often than every `20ms`.
 
-That's because they have different starting time, so "every 20ms" differs between different animations. The intervals are not alignned. So we'll have several independent runs within `20ms`.
+That's because they have different starting time, so "every 20ms" differs between different animations. The intervals are not aligned. So we'll have several independent runs within `20ms`.
 
 In other words, this:
 
@@ -75,7 +75,7 @@ setInterval(animate2, 20); // in different places of the script
 setInterval(animate3, 20);
 ```
 
-These several independent redraws should be grouped together, to make the redraw easier for the browser (and hence smoother for people).
+These several independent redraws should be grouped together, to make the redraw easier for the browser and hence load less CPU load and look smoother.
 
 There's one more thing to keep in mind. Sometimes when CPU is overloaded, or there are other reasons to redraw less often (like when the browser tab is hidden), so we really shouldn't run it every `20ms`.
 
diff --git a/8-web-components/3-shadow-dom/article.md b/8-web-components/3-shadow-dom/article.md
index 7a58dddb3..fafc4754c 100644
--- a/8-web-components/3-shadow-dom/article.md
+++ b/8-web-components/3-shadow-dom/article.md
@@ -35,9 +35,9 @@ input::-webkit-slider-runnable-track {
 <input type="range">
 ```
 
-Once again, `pseudo` is a non-standard attribute. Chronologically, browsers first started to experiment with internal DOM structures to implement controls, and then, after time, shadow DOM was standartized to allow us, developers, to do the similar thing.
+Once again, `pseudo` is a non-standard attribute. Chronologically, browsers first started to experiment with internal DOM structures to implement controls, and then, after time, shadow DOM was standardized to allow us, developers, to do the similar thing.
 
-Furhter on, we'll use the modern shadow DOM standard, covered by [DOM spec](https://dom.spec.whatwg.org/#shadow-trees) other related specifications.
+Further on, we'll use the modern shadow DOM standard, covered by [DOM spec](https://dom.spec.whatwg.org/#shadow-trees) other related specifications.
 
 ## Shadow tree
 
@@ -98,7 +98,7 @@ alert(elem.shadowRoot.host === elem); // true
 
 Shadow DOM is strongly delimited from the main document:
 
-1. Shadow DOM elements are not visible to `querySelector` from the light DOM. In particular,  Shadow DOM elements may have ids that conflict with those in the light DOM. They be unique only within the shadow tree.
+1. Shadow DOM elements are not visible to `querySelector` from the light DOM. In particular,  Shadow DOM elements may have ids that conflict with those in the light DOM. They must be unique only within the shadow tree.
 2. Shadow DOM has own stylesheets. Style rules from the outer DOM don't get applied.
 
 For example:
diff --git a/8-web-components/4-template-element/article.md b/8-web-components/4-template-element/article.md
index 4d9df9cb3..25aada6fc 100644
--- a/8-web-components/4-template-element/article.md
+++ b/8-web-components/4-template-element/article.md
@@ -1,9 +1,9 @@
 
 # Template element
 
-A built-in `<template>` element serves as a storage for markup. The browser ignores it contents, only checks for syntax validity, but we can access and use it in JavaScript, to create other elements.
+A built-in `<template>` element serves as a storage for HTML markup templates. The browser ignores it contents, only checks for syntax validity, but we can access and use it in JavaScript, to create other elements.
 
-In theory, we could create any invisible element somewhere in HTML for markup storage purposes. What's special about `<template>`?
+In theory, we could create any invisible element somewhere in HTML for HTML markup storage purposes. What's special about `<template>`?
 
 First, its content can be any valid HTML, even if it normally requires a proper enclosing tag.
 
@@ -31,9 +31,9 @@ We can put styles and scripts into `<template>` as well:
 </template>
 ```
 
-The browser considers `<template>` content "out of the document", so the style is not applied, scripts are executed, `<video autoplay>` is not run, etc.
+The browser considers `<template>` content "out of the document": styles are not applied, scripts are not executed, `<video autoplay>` is not run, etc.
 
-The content becomes live (the script executes) when we insert it.
+The content becomes live (styles apply, scripts run etc) when we insert it into the document.
 
 ## Inserting template
 
@@ -87,7 +87,7 @@ Let's rewrite a Shadow DOM example from the previous chapter using `<template>`:
 </script>
 ```
 
-In the line `(*)` when we clone and insert `tmpl.content`, its children (`<style>`, `<p>`) are inserted instead.
+In the line `(*)` when we clone and insert `tmpl.content`, as it's `DocumentFragment`, its children (`<style>`, `<p>`) are inserted instead.
 
 They form the shadow DOM:
 
@@ -109,8 +109,8 @@ To summarize:
 
 The `<template>` tag is quite unique, because:
 
-- The browser checks the syntax inside it (as opposed to using a template string inside a script).
+- The browser checks HTML syntax inside it (as opposed to using a template string inside a script).
 - ...But still allows to use any top-level HTML tags, even those that don't make sense without proper wrappers (e.g. `<tr>`).
 - The content becomes interactive: scripts run, `<video autoplay>` plays etc, when inserted into the document.
 
-The `<template>` tag does not feature any sophisticated iteration mechanisms, data binding or variable substitutions, making it less powerful than frameworks. But we can build those on top of it.
+The `<template>` element does not feature any iteration mechanisms, data binding or variable substitutions, but we can implement those on top of it.
diff --git a/9-regular-expressions/01-regexp-introduction/article.md b/9-regular-expressions/01-regexp-introduction/article.md
index 59775d3c0..57fe02f5d 100644
--- a/9-regular-expressions/01-regexp-introduction/article.md
+++ b/9-regular-expressions/01-regexp-introduction/article.md
@@ -1,13 +1,5 @@
 # Patterns and flags
 
-Regular expressions is a powerful way of searching and replacing inside a string.
-
-In JavaScript regular expressions are implemented using objects of a built-in `RegExp` class and integrated with strings.
-
-Please note that regular expressions vary between programming languages. In this tutorial we concentrate on JavaScript. Of course there's a lot in common, but they are a somewhat different in Perl, Ruby, PHP etc.
-
-## Regular expressions
-
 A regular expression (also "regexp", or just "reg") consists of a *pattern* and optional *flags*.
 
 There are two syntaxes to create a regular expression object.
@@ -85,7 +77,7 @@ alert( "<h1> <h2> <h3>".search(regexp));
 
 Regular expressions may have flags that affect the search.
 
-There are only 5 of them in JavaScript:
+There are only 6 of them in JavaScript:
 
 `i`
 : With this flag the search is case-insensitive: no difference between `A` and `a` (see the example below).
diff --git a/9-regular-expressions/03-regexp-character-classes/article.md b/9-regular-expressions/03-regexp-character-classes/article.md
index c1bc1bad5..592448c78 100644
--- a/9-regular-expressions/03-regexp-character-classes/article.md
+++ b/9-regular-expressions/03-regexp-character-classes/article.md
@@ -43,7 +43,7 @@ Most used are:
 : A space symbol: that includes spaces, tabs, newlines.
 
 `\w` ("w" is from "word")
-: A "wordly" character: either a letter of English alphabet or a digit or an underscore. Non-english letters (like cyrillic or hindi) do not belong to `\w`.
+: A "wordly" character: either a letter of English alphabet or a digit or an underscore. Non-Latin letters (like cyrillic or hindi) do not belong to `\w`.
 
 For instance, `pattern:\d\s\w` means a "digit" followed by a "space character" followed by a "wordly character", like `"1 a"`.
 
@@ -115,7 +115,7 @@ alert( "Hello, Java!".match(/\bJava!\b/) ); // null (no match)
 
 Once again let's note that `pattern:\b` makes the searching engine to test for the boundary, so that `pattern:Java\b` finds `match:Java` only when followed by a word boundary, but it does not add a letter to the result.
 
-Usually we use `\b` to find standalone English words. So that if we want `"Java"` language then `pattern:\bJava\b` finds exactly a standalone word and ignores it when it's a part of `"JavaScript"`.
+Usually we use `\b` to find standalone English words. So that if we want `"Java"` language then `pattern:\bJava\b` finds exactly a standalone word and ignores it when it's a part of another word, e.g. it won't match `match:Java` in `subject:JavaScript`.
 
 Another example: a regexp `pattern:\b\d\d\b` looks for standalone two-digit numbers. In other words, it requires that before and after `pattern:\d\d` must be a symbol different from `\w` (or beginning/end of the string).
 
@@ -123,8 +123,10 @@ Another example: a regexp `pattern:\b\d\d\b` looks for standalone two-digit numb
 alert( "1 23 456 78".match(/\b\d\d\b/g) ); // 23,78
 ```
 
-```warn header="Word boundary doesn't work for non-English alphabets"
+```warn header="Word boundary doesn't work for non-Latin alphabets"
 The word boundary check `\b` tests for a boundary between `\w` and something else. But `\w` means an English letter (or a digit or an underscore), so the test won't work for other characters (like cyrillic or hieroglyphs).
+
+Later we'll come by Unicode character classes that allow to solve the similar task for different languages.
 ```
 
 
@@ -223,13 +225,14 @@ alert( "CS4".match(/CS.4/) ); // null, no match because there's no character for
 
 Usually a dot doesn't match a newline character.
 
-For instance, this doesn't match:
+For instance, `pattern:A.B` matches `match:A`, and then `match:B` with any character between them, except a newline.
+
+This doesn't match:
 
 ```js run
 alert( "A\nB".match(/A.B/) ); // null (no match)
 
-// a space character would match
-// or a letter, but not \n
+// a space character would match, or a letter, but not \n
 ```
 
 Sometimes it's inconvenient, we really want "any character", newline included.
@@ -240,7 +243,6 @@ That's what `s` flag does. If a regexp has it, then the dot `"."` match literall
 alert( "A\nB".match(/A.B/s) ); // A\nB (match!)
 ```
 
-
 ## Summary
 
 There exist following character classes:
@@ -255,11 +257,13 @@ There exist following character classes:
 
 ...But that's not all!
 
-Modern JavaScript also allows to look for characters by their Unicode properties, for instance:
+The Unicode encoding, used by JavaScript for strings, provides many properties for characters, like: which language the letter belongs to (if a letter) it is it a punctuation sign, etc.
+
+Modern JavaScript allows to use these properties in regexps to look for characters, for instance:
 
 - A cyrillic letter is: `pattern:\p{Script=Cyrillic}` or `pattern:\p{sc=Cyrillic}`.
 - A dash (be it a small hyphen `-` or a long dash `—`): `pattern:\p{Dash_Punctuation}` or `pattern:\p{pd}`.
-- A currency symbol: `pattern:\p{Currency_Symbol}` or `pattern:\p{sc}`.
+- A currency symbol, such as `$`, `€` or another: `pattern:\p{Currency_Symbol}` or `pattern:\p{sc}`.
 - ...And much more. Unicode has a lot of character categories that we can select from.
 
 These patterns require `'u'` regexp flag to work. More about that in the chapter [](info:regexp-unicode).
diff --git a/9-regular-expressions/04-regexp-escaping/article.md b/9-regular-expressions/04-regexp-escaping/article.md
index 48f4a810d..909cd4856 100644
--- a/9-regular-expressions/04-regexp-escaping/article.md
+++ b/9-regular-expressions/04-regexp-escaping/article.md
@@ -61,7 +61,7 @@ let reg = new RegExp("\d\.\d");
 alert( "Chapter 5.1".match(reg) ); // null
 ```
 
-It worked with `pattern:/\d\.\d/`, but with `new RegExp("\d\.\d")` it doesn't, why?
+The search worked with `pattern:/\d\.\d/`, but with `new RegExp("\d\.\d")` it doesn't work, why?
 
 The reason is that backslashes are "consumed" by a string. Remember, regular strings have their own special characters like `\n`, and a backslash is used for escaping.
 
@@ -77,7 +77,7 @@ The quotes "consume" backslashes and interpret them, for instance:
 - `\u1234` -- becomes the Unicode character with such code,
 - ...And when there's no special meaning: like `\d` or `\z`, then the backslash is simply removed.
 
-So the call to `new RegExp` gets a string without backslashes. That's why it doesn't work!
+So the call to `new RegExp` gets a string without backslashes. That's why the search doesn't work!
 
 To fix it, we need to double backslashes, because quotes turn `\\` into `\`:
 
diff --git a/9-regular-expressions/05-regexp-character-sets-and-ranges/article.md b/9-regular-expressions/05-regexp-character-sets-and-ranges/article.md
index 5c8a8babb..7204f2b1c 100644
--- a/9-regular-expressions/05-regexp-character-sets-and-ranges/article.md
+++ b/9-regular-expressions/05-regexp-character-sets-and-ranges/article.md
@@ -15,7 +15,7 @@ alert( "Mop top".match(/[tm]op/gi) ); // "Mop", "top"
 
 Please note that although there are multiple characters in the set, they correspond to exactly one character in the match.
 
-So the example above gives no matches:
+So the example below gives no matches:
 
 ```js run
 // find "V", then [o or i], then "la"
@@ -58,7 +58,7 @@ We can use character classes inside `[…]` as well.
 
 For instance, we want to match all wordly characters or a dash, for words like "twenty-third". We can't do it with `pattern:\w+`, because `pattern:\w` class does not include a dash. But we can use `pattern:[\w-]`.
 
-We also can use a combination of classes to cover every possible character, like `pattern:[\s\S]`. That matches spaces or non-spaces -- any character. That's wider than a dot `"."`, because the dot matches any character except a newline.
+We also can use several classes, for example `pattern:[\s\S]` matches spaces or non-spaces -- any character. That's wider than a dot `"."`, because the dot matches any character except a newline (unless `s` flag is set).
 
 ## Excluding ranges
 
diff --git a/9-regular-expressions/08-regexp-greedy-and-lazy/4-find-html-tags-greedy-lazy/task.md b/9-regular-expressions/08-regexp-greedy-and-lazy/4-find-html-tags-greedy-lazy/task.md
index 2cf48a4ae..e3c39c373 100644
--- a/9-regular-expressions/08-regexp-greedy-and-lazy/4-find-html-tags-greedy-lazy/task.md
+++ b/9-regular-expressions/08-regexp-greedy-and-lazy/4-find-html-tags-greedy-lazy/task.md
@@ -12,4 +12,4 @@ let str = '<> <a href="/"> <input type="radio" checked> <b>';
 alert( str.match(reg) ); // '<a href="/">', '<input type="radio" checked>', '<b>'
 ```
 
-Let's assume that may not contain `<` and `>` inside (in quotes too), that simplifies things a bit. 
+Here we assume that tag attributes may not contain `<` and `>` (inside squotes too), that simplifies things a bit. 
diff --git a/9-regular-expressions/08-regexp-greedy-and-lazy/article.md b/9-regular-expressions/08-regexp-greedy-and-lazy/article.md
index f7c6de43d..149e08ec9 100644
--- a/9-regular-expressions/08-regexp-greedy-and-lazy/article.md
+++ b/9-regular-expressions/08-regexp-greedy-and-lazy/article.md
@@ -264,7 +264,7 @@ That's what's going on:
 2. Then it looks for `pattern:.*?`: takes one character (lazily!), check if there's a match for `pattern:" class="doc">` (none).
 3. Then takes another character into `pattern:.*?`, and so on... until it finally reaches `match:" class="doc">`.
 
-But the problem is: that's already beyound the link, in another tag `<p>`. Not what we want.
+But the problem is: that's already beyond the link, in another tag `<p>`. Not what we want.
 
 Here's the picture of the match aligned with the text:
 
diff --git a/9-regular-expressions/15-regexp-infinite-backtracking-problem/article.md b/9-regular-expressions/15-regexp-infinite-backtracking-problem/article.md
index 54bbccd9b..9eb1824d3 100644
--- a/9-regular-expressions/15-regexp-infinite-backtracking-problem/article.md
+++ b/9-regular-expressions/15-regexp-infinite-backtracking-problem/article.md
@@ -26,7 +26,7 @@ We want to find all tags, with or without attributes -- like `subject:<a href=".
 
 In particular, we need it to match tags like `<a test="<>" href="#">` -- with `<` and `>` in attributes. That's allowed by [HTML standard](https://html.spec.whatwg.org/multipage/syntax.html#syntax-attributes).
 
-Now we can see that a simple regexp like `pattern:<[^>]+>` doesn't work, because it stops at the first `>`, and we need to ignore `<>` if inside an attribute.
+A simple regexp like `pattern:<[^>]+>` doesn't work, because it stops at the first `>`, and we need to ignore `<>` if inside an attribute:
 
 ```js run
 // the match doesn't reach the end of the tag - wrong!
@@ -41,7 +41,7 @@ To correctly handle such situations we need a more complex regular expression. I
 
 If we substitute these into the pattern above and throw in some optional spaces `pattern:\s`, the full regexp becomes: `pattern:<\w+(\s*\w+="[^"]*"\s*)*>`.
 
-That regexp is not perfect! It doesn't yet support all details of HTML, for instance unquoted values, and there are other ways to improve, but let's not add complexity. It will demonstrate the problem for us.
+That regexp is not perfect! It doesn't support all the details of HTML syntax, such as unquoted values, and there are other ways to improve, but let's not add complexity. It will demonstrate the problem for us.
 
 The regexp seems to work:
 
@@ -222,6 +222,8 @@ The string has no `>` at the end, so the match is impossible, but the regexp eng
 ...
 ```
 
+As there are many combinations, it takes a lot of time.
+
 ## How to fix?
 
 The backtracking checks many variants that are an obvious fail for a human.
diff --git a/9-regular-expressions/20-regexp-unicode/article.md b/9-regular-expressions/20-regexp-unicode/article.md
index 68eebca8b..95fac0fbb 100644
--- a/9-regular-expressions/20-regexp-unicode/article.md
+++ b/9-regular-expressions/20-regexp-unicode/article.md
@@ -80,7 +80,7 @@ If we forget the `u` flag and occasionally use surrogate pairs, then we can get
 
 Normally, regexps understand `[a-z]` as a "range of characters with codes between codes of `a` and `z`.
 
-But without `u` flag, surrogate pairs are assumed to be a "pair of independant characters", so `[𝒳-𝒴]` is like `[<55349><56499>-<55349><56500>]` (replaced each surrogate pair with code points). Now we can clearly see that the range `56499-55349` is unacceptable, as the left range border must be less than the right one.
+But without `u` flag, surrogate pairs are assumed to be a "pair of independent characters", so `[𝒳-𝒴]` is like `[<55349><56499>-<55349><56500>]` (replaced each surrogate pair with code points). Now we can clearly see that the range `56499-55349` is unacceptable, as the left range border must be less than the right one.
 
 Using the `u` flag makes it work right:
 
diff --git a/9-regular-expressions/21-regexp-unicode-properties/article.md b/9-regular-expressions/21-regexp-unicode-properties/article.md
index eac9bfbca..908550999 100644
--- a/9-regular-expressions/21-regexp-unicode-properties/article.md
+++ b/9-regular-expressions/21-regexp-unicode-properties/article.md
@@ -1,5 +1,5 @@
 
-# Unicode character properies \p
+# Unicode character properties \p
 
 [Unicode](https://en.wikipedia.org/wiki/Unicode), the encoding format used by JavaScript strings, has a lot of properties for different characters (or, technically, code points). They describe which "categories" character belongs to, and a variety of technical details.
 
@@ -12,7 +12,7 @@ Here's the main tree of properties:
 - Letter `L`:
   - lowercase `Ll`, modifier `Lm`, titlecase `Lt`, uppercase `Lu`, other `Lo`
 - Number `N`:
-  - decimal digit `Nd`, letter number `Nl`, other `No`:
+  - decimal digit `Nd`, letter number `Nl`, other `No`
 - Punctuation `P`:
   - connector `Pc`, dash `Pd`, initial quote `Pi`, final quote `Pf`, open `Ps`, close `Pe`, other `Po`
 - Mark `M` (accents etc):
@@ -22,7 +22,7 @@ Here's the main tree of properties:
 - Separator `Z`:
   - line `Zl`, paragraph `Zp`, space `Zs`
 - Other `C`:
-  - control `Cc`, format `Cf`, not assigned `Cn`, private use `Co`, surrogate `Cs`.
+  - control `Cc`, format `Cf`, not assigned `Cn`, private use `Co`, surrogate `Cs`
 
 ```smart header="More information"
 Interested to see which characters belong to a property? There's a tool at <http://cldr.unicode.org/unicode-utilities/list-unicodeset> for that.
@@ -40,14 +40,14 @@ There are also other derived categories, like:
 For instance, let's look for a 6-digit hex number:
 
 ```js run
-let reg = /\p{Hex_Digit}{6}/u; // flag 'u' is requireds
+let reg = /\p{Hex_Digit}{6}/u; // flag 'u' is required
 
 alert("color: #123ABC".match(reg)); // 123ABC
 ```
 
 There are also properties with a value. For instance, Unicode "Script" (a writing system) can be Cyrillic, Greek, Arabic, Han (Chinese) etc, the [list is long]("https://en.wikipedia.org/wiki/Script_(Unicode)").
 
-To search for certain scripts, we should supply `Script=<value>`, e.g. to search for cyrillic letters: `\p{sc=Cyrillic}`, for Chinese glyphs: `\p{sc=Han}`, etc:
+To search for characters in certain scripts ("alphabets"), we should supply `Script=<value>`, e.g. to search for cyrillic letters: `\p{sc=Cyrillic}`, for Chinese glyphs: `\p{sc=Han}`, etc:
 
 ```js run
 let regexp = /\p{sc=Han}+/gu; // get chinese words
@@ -59,15 +59,15 @@ alert( str.match(regexp) ); // 你好
 
 ## Building multi-language \w
 
-Let's make a "universal" regexp for `pattern:\w`, for any language. That task has a standard solution in many programming languages with unicode-aware regexps, e.g. Perl.
+The pattern `pattern:\w` means "wordly characters", but doesn't work for languages that use non-Latin alphabets, such as Cyrillic and others. It's just a shorthand for `[a-zA-Z0-9_]`, so `pattern:\w+` won't find any Chinese words etc.
+
+Let's make a "universal" regexp, that looks for wordly characters in any language. That's easy to do using Unicode properties:
 
 ```js
 /[\p{Alphabetic}\p{Mark}\p{Decimal_Number}\p{Connector_Punctuation}\p{Join_Control}]/u
 ```
 
-Let's decipher. Remember, `pattern:\w` is actually the same as `pattern:[a-zA-Z0-9_]`.
-
-So the character set includes:
+Let's decipher. Just as `pattern:\w` is the same as `pattern:[a-zA-Z0-9_]`, we're making a set of our own, that includes:
 
 - `Alphabetic` for letters,
 - `Mark` for accents, as in Unicode accents may be represented by separate code points,
diff --git a/9-regular-expressions/22-regexp-sticky/article.md b/9-regular-expressions/22-regexp-sticky/article.md
index 5a790bb31..57c7a0b1f 100644
--- a/9-regular-expressions/22-regexp-sticky/article.md
+++ b/9-regular-expressions/22-regexp-sticky/article.md
@@ -7,7 +7,7 @@ One of common tasks for regexps is "parsing": when we get a text and analyze it
 
 For instance, there are HTML parsers for browser pages, that turn text into a structured document. There are parsers for programming languages, like JavaScript, etc.
 
-Writing parsers is a special area, with its own tools and algorithms, so we don't go deep in there, but there's a very common question: "What is the text at the given position?".
+Writing parsers is a special area, with its own tools and algorithms, so we don't go deep in there, but there's a very common question in them, and, generally, for text analysis: "What kind of entity is at the given position?".
 
 For instance, for a programming language variants can be like:
 - Is it a "name" `pattern:\w+`?
@@ -15,9 +15,13 @@ For instance, for a programming language variants can be like:
 - Or an operator `pattern:[+-/*]`?
 - (a syntax error if it's not anything in the expected list)
 
-In JavaScript, to perform a search starting from a given position, we can use `regexp.exec` with `regexp.lastIndex` property, but that's not what we need!
+So, we should try to match a couple of regular expressions, and make a decision what's at the given position.
 
-We'd like to check the match exactly at given position, not "starting" from it.
+In JavaScript, how can we perform a search starting from a given position? Regular calls start searching from the text start.
+
+We'd like to avoid creating substrings, as this slows down the execution considerably.
+
+One option is to use `regexp.exec` with `regexp.lastIndex` property, but that's not what we need, as this would search the text starting from `lastIndex`, while we only need to text the match *exactly* at the given position.
 
 Here's a (failing) attempt to use `lastIndex`:
 
@@ -33,13 +37,11 @@ alert (regexp.exec(str)); // function
 
 The match is found, because `regexp.exec` starts to search from the given position and goes on by the text, successfully matching "function" later.
 
-We could work around that by checking if "`regexp.exec(str).index` property is `5`, and if not, ignore the much. But the main problem here is performance.
-
-The regexp engine does a lot of unnecessary work by scanning at further positions. The delays are clearly noticeable if the text is long, because there are many such searches in a parser.
+We could work around that by checking if "`regexp.exec(str).index` property is `5`, and if not, ignore the match. But the main problem here is performance. The regexp engine does a lot of unnecessary work by scanning at further positions. The delays are clearly noticeable if the text is long, because there are many such searches in a parser.
 
 ## The "y" flag
 
-So we've came to the problem: how to search for a match, starting exactly at the given position.
+So we've came to the problem: how to search for a match exactly at the given position.
 
 That's what `y` flag does. It makes the regexp search only at the `lastIndex` position.
 
@@ -66,6 +68,6 @@ As we can see, now the regexp is only matched at the given position.
 
 So what `y` does is truly unique, and very important for writing parsers.
 
-The `y` flag allows to apply a regular expression (or many of them one-by-one) exactly at the given position and when we understand what's there, we can move on -- step by step examining the text.
+The `y` flag allows to test a regular expression exactly at the given position and when we understand what's there, we can move on -- step by step examining the text.
 
 Without the flag the regexp engine always searches till the end of the text, that takes time, especially if the text is large. So our parser would be very slow. The `y` flag is exactly the right thing here.
diff --git a/9-regular-expressions/index.md b/9-regular-expressions/index.md
index ac25aaa67..7499c584d 100644
--- a/9-regular-expressions/index.md
+++ b/9-regular-expressions/index.md
@@ -1,3 +1,7 @@
 # Regular expressions
 
 Regular expressions is a powerful way of doing search and replace in strings.
+
+In JavaScript regular expressions are implemented using objects of a built-in `RegExp` class and integrated with strings.
+
+Please note that regular expressions vary between programming languages. In this tutorial we concentrate on JavaScript. Of course there's a lot in common, but they are a somewhat different in Perl, Ruby, PHP etc.
diff --git a/LICENSE.md b/LICENSE.md
index 60f06924e..ea5012f37 100644
--- a/LICENSE.md
+++ b/LICENSE.md
@@ -1,5 +1,11 @@
 
-# Attribution-NonCommercial-ShareAlike 4.0
+The tutorial is free to read.
+
+If you'd like to do something else with it, please get a permission from Ilya Kantor, iliakan@javascript.ru.
+
+As of now, we license the tutorial to almost everyone for free under the terms of an "open" CC-BY-NC-SA license. Just please be so kind to contact me.
+
+## Attribution-NonCommercial-ShareAlike license (CC-BY-NC-SA)
 
 The full license text is at <https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode>.
 
diff --git a/README.md b/README.md
index 945ba4831..45f091977 100755
--- a/README.md
+++ b/README.md
@@ -6,6 +6,7 @@ Articles can be in Brazilian or European Portuguese, but not mixed. Translators
 
 **That's how you can contribute:**
 
+<<<<<<< HEAD
 - See the [Portuguese Translate Progress](https://github.com/javascript-tutorial/pt.javascript.info/issues/1) issue.
 - Choose an unchecked article you'd like to translate.
 - Add a comment with the article title to the issue, e.g. `An Introduction to JavaScript`.
@@ -13,6 +14,9 @@ Articles can be in Brazilian or European Portuguese, but not mixed. Translators
     - Your comment should contain only the title.
 - Fork the repository, translate and send a PR when done.
     - PR title should match article title, the bot will write it's number into the issue.
+=======
+See <https://javascript.info/translate> for the details.
+>>>>>>> 08734734021aa128c13da2382fe8fa062677bb9f
 
 Please kindly allow maintainers to review and merge or request changes in your translation.
    
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index c740ac577..bebfcd3ec 100644
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