[docs] update endpoint documentation (#4060)

* [docs] update endpoint documentation

* Update documentation/docs/01-routing.md

Co-authored-by: Rich Harris <richard.a.harris@gmail.com>

* Update documentation/docs/01-routing.md

Co-authored-by: Rich Harris <richard.a.harris@gmail.com>

* Update documentation/docs/01-routing.md

Co-authored-by: Rich Harris <richard.a.harris@gmail.com>

documentation/docs/01-routing.md

@@ -45,9 +45,7 @@ A file or directory can have multiple dynamic parts, like `[id]-[category].svelt
 
 ### Endpoints
 
-Endpoints are modules written in `.js` (or `.ts`) files that export functions corresponding to HTTP methods. Their job is to allow pages to read and write data that is only available on the server (for example in a database, or on the filesystem).
-
-If an endpoint has the same filename as a page (except for the extension), the page will get its props from the endpoint. So a page like `src/routes/items/[id].svelte` could get its props from this file:
+Endpoints are modules written in `.js` (or `.ts`) files that export [request handler](/docs/types#sveltejs-kit-requesthandler) functions corresponding to HTTP methods. Their job is to make it possible to read and write data that is only available on the server (for example in a database, or on the filesystem).
 
 ```js
 /// file: src/routes/items/[id].js
@@ -81,7 +79,7 @@ export async function get({ params }) {
 
 > All server-side code, including endpoints, has access to `fetch` in case you need to request data from external APIs. Don't worry about the `$lib` import, we'll get to that [later](/docs/modules#$lib).
 
-The job of this function is to return a `{ status, headers, body }` object representing the response, where `status` is an [HTTP status code](https://httpstatusdogs.com):
+The job of a [request handler](/docs/types#sveltejs-kit-requesthandler) is to return a `{ status, headers, body }` object representing the response, where `status` is an [HTTP status code](https://httpstatusdogs.com):
 
 - `2xx` — successful response (default is `200`)
 - `3xx` — redirection (should be accompanied by a `location` header)
@@ -90,7 +88,11 @@ The job of this function is to return a `{ status, headers, body }` object repre
 
 > If `{fallthrough: true}` is returned SvelteKit will [fall through](/docs/routing#advanced-routing-fallthrough-routes) to other routes until something responds, or will respond with a generic 404.
 
-The returned `body` corresponds to the page's props:
+#### Page endpoints
+
+If an endpoint has the same filename as a page (except for the extension), the page gets its props from the endpoint — via `fetch` during client-side navigation, or via direct function call during SSR.
+
+A page like `src/routes/items/[id].svelte` could get its props from the `body` in the endpoint above:
 
 ```svelte
 /// file: src/routes/items/[id].svelte
@@ -102,6 +104,23 @@ The returned `body` corresponds to the page's props:
 <h1>{item.title}</h1>
 ```
 
+Because the page and route have the same URL, you will need to include an `accept: application/json` header to get JSON from the endpoint rather than HTML from the page. You can also get the raw data by appending `/__data.json` to the URL, e.g. `/items/__data.json`.
+
+#### Standalone endpoints
+
+Most commonly, endpoints exist to provide data to the page with which they're paired. They can, however, exist separately from pages. Standalone endpoints have slightly more flexibility over the returned `body` type — in addition to objects, they can return a `Uint8Array`.
+
+Standalone endpoints can be given a file extension if desired, or accessed directly if not:
+
+| filename                      | endpoint   |
+| ----------------------------- | ---------- |
+| src/routes/data/index.json.js | /data.json |
+| src/routes/data.json.js       | /data.json |
+| src/routes/data/index.js      | /data      |
+| src/routes/data.js            | /data      |
+
+> Support for streaming request and response bodies is [coming soon](https://github.com/sveltejs/kit/issues/3419).
+
 #### POST, PUT, PATCH, DELETE
 
 Endpoints can handle any HTTP method — not just `GET` — by exporting the corresponding function:
@@ -191,8 +210,6 @@ export async function post({ request }) {
 </form>
 ```
 
-If you request the route with an `accept: application/json` header, SvelteKit will render the endpoint data as JSON, rather than the page as HTML. You can also get the raw data by appending `/__data.json` to the URL, e.g. `/items/__data.json`.
-
 #### Body parsing
 
 The `request` object is an instance of the standard [Request](https://developer.mozilla.org/en-US/docs/Web/API/Request) class. As such, accessing the request body is easy:
@@ -263,21 +280,6 @@ export default config;
 
 > Using native `<form>` behaviour ensures your app continues to work when JavaScript fails or is disabled.
 
-### Standalone endpoints
-
-Most commonly, endpoints exist to provide data to the page with which they're paired. They can, however, exist separately from pages. Standalone endpoints have slightly more flexibility over the returned `body` type — in addition to objects, they can return a string or a `Uint8Array`.
-
-> Support for streaming request and response bodies is [coming soon](https://github.com/sveltejs/kit/issues/3419).
-
-Standalone endpoints can be given a file extension if desired, or accessed directly if not:
-
-| filename                      | endpoint   |
-| ----------------------------- | ---------- |
-| src/routes/data/index.json.js | /data.json |
-| src/routes/data.json.js       | /data.json |
-| src/routes/data/index.js      | /data      |
-| src/routes/data.js            | /data      |
-
 ### Private modules
 
 Files and directories with a leading `_` or `.` (other than [`.well-known`](https://en.wikipedia.org/wiki/Well-known_URI)) are private by default, meaning that they do not create routes (but can be imported by files that do). You can configure which modules are considered public or private with the [`routes`](/docs/configuration#routes) configuration.