Creating or Extending an Edit Mode

Kyle J. Kemp edited this page May 14, 2016 · 28 revisions

Creating a new Edit Mode

The best way to create a new edit mode, is to extend an existing one.

Minimal new mode

define('ace/mode/example', function(require, exports, module) {

var oop = require("ace/lib/oop");
var TextMode = require("ace/mode/text").Mode;
var ExampleHighlightRules = require("ace/mode/example_highlight_rules").ExampleHighlightRules;

var Mode = function() {
    this.HighlightRules = ExampleHighlightRules;
oop.inherits(Mode, TextMode);

(function() {
    // Extra logic goes here. (see below)

exports.Mode = Mode;

define('ace/mode/example_highlight_rules', function(require, exports, module) {

var oop = require("ace/lib/oop");
var TextHighlightRules = require("ace/mode/text_highlight_rules").TextHighlightRules;

var ExampleHighlightRules = function() {

    this.$rules = new TextHighlightRules().getRules();

oop.inherits(ExampleHighlightRules, TextHighlightRules);

exports.ExampleHighlightRules = ExampleHighlightRules;

Extending the Mode

getNextLineIndent(state, line, tab) { }

Called with each new line, state is the name of the current highlighter state, line the complete text of the current line, and tab is the tab filler currently on the editor (e.g. 4 spaces, or a tab character). Returns a string which is appended to the new line.

createWorker(session) { }

This is called on session creation to start a worker which can perform analysis in the background, commonly annotations for highlighting errors in syntax. It should create and return a worker using the WorkerClient function. A full example can be seen in ace/mode/javascript.

checkOutdent(state, line, input)

input here is the character sequence entered. Should return true or false on whether to call autoOutdent().

autoOutdent(state, doc, row)

This function when called should perform any replacement needed to outdent the current line. A full example can be seen in ace/mode/matching_brace_outdent.

toggleCommentLines(state, doc, startRow, endRow)

Extending the Highlighter

The highlighter functions as a state machine, with regex matches used to determine tokens and transitions between states. These notes assume use of the latest Ace.

Highlighter Rules

A highlighters rules have the layout:

this.$rules = {
    stateName: [ {
        token: <token>, // String, Array, or Function
        regex: <regex>, // String
        next:  <next>   // Optional, String
    } ]

The highlighter starts off in the "start" state. Tokens are strings, and tag the text with classes of the form ace_token. Multiple tokens can be applied to the same text by adding dots in the token, eg support.function will add the classes ace_support ace_function.

A regex can either be a flat regex (abc) or have matching groups ((a+)(b+)). There is a strict requirement that if matching groups are used, then they must cover the entire matched string ((hel)lo is invalid.)

For flat regex matches, token should be a String, or a Function that takes a single argument (the match) and returns a string token.

For grouped regex, token can be a String, in which case all matched groups are given that same token. It can be an Array (of the same length as the number of groups), whereby matches are given the token of the same alignment as in the match. For a function, the Function should take the same number of arguments as there are groups, and return an array of tokens as per before.

// Example rules:

  token : "constant",
  regex : "INT_MAX|INT_MIN"
} // INT_MAX -> constant(INT_MAX)

  token : ["constant", "keyword"],
  regex : "^(#{1,6})(.+)$"
} // ### Header -> constant(###), keyword( Header)

  token : "constant",
  regex : "(a+)(b)(\\1)"
} // aabaa -> constant(aabaa) :: abaa -> constant(aba) + a

  token : function (first, second) {
    if (first == "a") return ["constant", "keyword"];
    return ["keyword", "constant"];
  regex: "(.)(world)"
} // aworld -> constant(a), keyword(world) :: bworld -> keyword(a), constant(world)

If a rule is matched which has a next state set, then the tokeniser will move into that new state. Rules are prioritised based on their position within the ruleset, and the usual matching rules for regex apply. (eg of the rules (a)(b) and .+ applied to the string cab, .+ will match even if (a)(b) is higher priority).

Highlighter Helper Functions


Returns the rules for a highlighter.

addRules(rules, prefix)

Adds a set of rules, prefixing all state names with the given prefix.

this.$rules = {
    start: [ /* ... */ ]

var newRules = {
    start: [ /* ... */ ]

this.addRules(newRules, "new-");

    this.$rules == {
        start: [ ... ],
        "new-start": [ ... ]

Embedding a different highlighter

Using embedRules it is easy to embed one highlighter within another. For instance, to embed css highlighting between ^style and ^endstyle:

var CssHighlightRules = require("ace/mode/css_highlight_rules").CssHighlightRules;

this.$rules = {
    start: [ {
        token: "keyword",
        regex: "^style\\s*$",
        next: "css-start"
    } ]

this.embedRules(CssHighlightRules, "css-", [{
   token : "keyword",
   regex: "^endstyle\\s*$",
   next  : "start"

Mode delegation

Once a highlighter is embedded, it is also easy to delegate mode behaviour to the embedded mode while we are editing inside it. This is done by modifying the Mode constructor to use the getEmbeds and createModeDelegates functions as follows:

var CssMode = require("ace/mode/css").Mode;

var Mode = function() {
    var highlighter = new ExampleHighlightRules();
    this.$tokenizer = new Tokenizer(highlighter.getRules());
    this.$embeds = highlighter.getEmbeds();
      "css-": CssMode

With this, any mode specific behaviour (such as indenting, outdenting, or keyboard reactions) will be delegated to the CssMode when we are inside a css block. The prefix in createModeDelegates should match the one used in the highlighter. Multiple modes may be embedded in this manner, and the delegation is nestable, so that a JavaScriptMode inside an HTMLMode inside a MarkdownMode would still retain proper expected behaviour.

Common Tokens

The following are the common tokens to themes, taken from the TextMate manual. Note that not all of these may have styling associated with them, depending on the theme used.

  • comment: for comments.

    • line: line comments, we specialize further so that the type of comment start character(s) can be extracted from the scope.
      • double-slash: // comment
      • double-dash: -- comment
      • number-sign: # comment
      • percentage: % comment
      • character: other types of line comments.
    • block: multi-line comments like /* ... */ and <!-- ... -->.
      • documentation: embedded documentation.
  • constant: various forms of constants.

    • numeric: those which represent numbers, e.g. 42, 1.3f, 0x4AB1U.
    • character: those which represent characters, e.g. &lt;, \e, \031.
      • escape: escape sequences like \e would be constant.character.escape.
    • language: constants (generally) provided by the language which are "special" like true, false, nil, YES, NO, etc.
    • other: other constants, e.g. colors in CSS.
  • entity: an entity refers to a larger part of the document, for example a chapter, class, function, or tag. We do not scope the entire entity as entity.* (we use meta.* for that). But we do use entity.* for the "placeholders" in the larger entity, e.g. if the entity is a chapter, we would use for the chapter title.

    • name: we are naming the larger entity.
      • function: the name of a function.
      • type: the name of a type declaration or class.
      • tag: a tag name.
      • section: the name is the name of a section/heading.
    • other: other entities.
      • inherited-class: the superclass/baseclass name.
      • attribute-name: the name of an attribute (mainly in tags).
  • invalid: stuff which is "invalid."

    • illegal: illegal, e.g. an ampersand or lower-than character in HTML (which is not part of an entity/tag).
    • deprecated: for deprecated stuff e.g. using an API function which is deprecated or using styling with strict HTML.
  • keyword: keywords (when these do not fall into the other groups).

    • control: mainly related to flow control like continue, while, return, etc.
    • operator: operators can either be textual (e.g. or) or be characters.
    • other: other keywords.
  • markup: this is for markup languages and generally applies to larger subsets of the text.

    • underline: underlined text.
      • link: this is for links, as a convenience this is derived from markup.underline so that if there is no theme rule which specifically targets then it will inherit the underline style.
    • bold: bold text (text which is strong and similar should preferably be derived from this name).
    • heading: a section header. Optionally provide the heading level as the next element, for example markup.heading.2.html for <h2>...</h2> in HTML.
    • italic: italic text (text which is emphasized and similar should preferably be derived from this name).
    • list: list items.
      • numbered: numbered list items.
      • unnumbered: unnumbered list items.
    • quote: quoted (sometimes block quoted) text.
    • raw: text which is verbatim, e.g. code listings. Normally spell checking is disabled for markup.raw.
    • other: other markup constructs.
  • meta — the meta scope is generally used to markup larger parts of the document. For example the entire line which declares a function would be meta.function and the subsets would be storage.type,, variable.parameter etc. and only the latter would be styled. Sometimes the meta part of the scope will be used only to limit the more general element that is styled, most of the time meta scopes are however used in scope selectors for activation of bundle items. For example in Objective-C there is a meta scope for the interface declaration of a class and the implementation, allowing the same tab-triggers to expand differently, depending on context.

  • storage — things relating to “storage”.

    • type — the type of something, class, function, int, var, etc.
    • modifier — a storage modifier like static, final, abstract, etc.
  • string — strings.

    • quoted — quoted strings.
    • single — single quoted strings: 'foo'.
    • double — double quoted strings: "foo".
    • triple — triple quoted strings: """Python""".
    • other — other types of quoting: $'shell', %s{...}.
    • unquoted — for things like here-docs and here-strings.
    • interpolated — strings which are “evaluated”: `date`, $(pwd).
    • regexp — regular expressions: /(\w+)/.
    • other — other types of strings (should rarely be used).
  • support — things provided by a framework or library should be below support.

    • function — functions provided by the framework/library. For example NSLog in Objective-C is support.function.
    • class — when the framework/library provides classes.
    • type — types provided by the framework/library, this is probably only used for languages derived from C, which has typedef (and struct). Most other languages would introduce new types as classes.
    • constant — constants (magic values) provided by the framework/library.
    • variable — variables provided by the framework/library. For example NSApp in AppKit.
    • other — the above should be exhaustive, but for everything else use support.other.
  • variable — variables. Not all languages allow easy identification (and thus markup) of these.

    • parameter — when the variable is declared as the parameter.
    • language — reserved language variables like this, super, self, etc.
    • other — other variables, like $some_variables.
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