docs: document the spec deviations in web apis (denoland#8489)

docs/runtime.md

@@ -4,26 +4,13 @@ Documentation for all runtime functions (Web APIs + `Deno` global) can be found
 on
 [`doc.deno.land`](https://doc.deno.land/https/github.com/denoland/deno/releases/latest/download/lib.deno.d.ts).
 
-## Web APIs
+## Web Platform APIs
 
 For APIs where a web standard already exists, like `fetch` for HTTP requests,
 Deno uses these rather than inventing a new proprietary API.
 
-The detailed documentation for implemented Web APIs can be found on
-[doc.deno.land](https://doc.deno.land/https/raw.githubusercontent.com/denoland/deno/master/cli/dts/lib.deno.shared_globals.d.ts).
-Additionally, a full list of the Web APIs which Deno implements is also
-available
-[in the repository](https://github.com/denoland/deno/blob/$CLI_VERSION/cli/rt/README.md).
-
-The TypeScript definitions for the implemented web APIs can be found in the
-[`lib.deno.shared_globals.d.ts`](https://github.com/denoland/deno/blob/$CLI_VERSION/cli/dts/lib.deno.shared_globals.d.ts)
-and
-[`lib.deno.window.d.ts`](https://github.com/denoland/deno/blob/$CLI_VERSION/cli/dts/lib.deno.window.d.ts)
-files.
-
-Definitions that are specific to workers can be found in the
-[`lib.deno.worker.d.ts`](https://github.com/denoland/deno/blob/$CLI_VERSION/cli/dts/lib.deno.worker.d.ts)
-file.
+For more details, view the chapter on
+[Web Platform APIs](./runtime/web_platform_apis.md).
 
 ## `Deno` global
 

docs/runtime/web_platform_apis.md

@@ -0,0 +1,97 @@
+# Web Platform APIs
+
+Deno aims to use web platform APIs (like `fetch`) instead of inventing a new
+proprietary API where it makes sense. These APIs generally follow the
+specifications and should match the implementation in Chrome and Firefox. In
+some cases it makes sense to deviate from the spec slightly, because of the
+different security model Deno has.
+
+Here is a list of web platform APIs Deno implements:
+
+## `fetch` API
+
+### Overview
+
+The `fetch` API can be used to make HTTP requests. It is implemented as
+specified in the [WHATWG `fetch` spec](https://fetch.spec.whatwg.org/).
+
+You can find documentation about this API on
+[MDN](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API).
+
+### Spec deviations
+
+- The Deno user agent does not have a cookie jar. As such, the `set-cookie`
+  header on a response is not processed, or filtered from the visible response
+  headers.
+- Deno does not follow the same-origin policy, because the Deno user agent
+  currently does not have the concept of origins, and it does not have a cookie
+  jar. This means Deno does not need to protect against leaking authenticated
+  data cross origin. Because of this Deno does not implement the following
+  sections of the WHATWG `fetch` specification:
+  - Section `3.1. 'Origin' header`.
+  - Section `3.2. CORS protocol`.
+  - Section `3.5. CORB`.
+  - Section `3.6. 'Cross-Origin-Resource-Policy' header`.
+  - `Atomic HTTP redirect handling`.
+  - The `opaqueredirect` response type.
+- A `fetch` with a `redirect` mode of `manual` will return a `basic` response
+  rather than an `opaqueredirect` response.
+
+## `CustomEvent`, `EventTarget` and `EventListener`
+
+### Overview
+
+The DOM Event API can be used to dispatch and listen to events happening in an
+application. It is implemented as specified in the
+[WHATWG DOM spec](https://dom.spec.whatwg.org/#events).
+
+You can find documentation about this API on
+[MDN](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget).
+
+### Spec deviations
+
+- Events do not bubble, because Deno does not have a DOM hierarchy, so there is
+  no tree for Events to bubble/capture through.
+
+## Web Worker API
+
+### Overview
+
+The WebWorker API can be used to executing code in a separate thread. It is
+implemented as specified in the
+[WHATWG HTML spec](https://html.spec.whatwg.org/multipage/workers.html#workers).
+
+You can find documentation about this API on
+[MDN](https://developer.mozilla.org/en-US/docs/Web/API/Worker).
+
+### Spec deviations
+
+- Currently creating workers from blob URLs is not supported.
+- Currently posted data is serialized to JSON instead of structured cloning.
+- Currently object ownership cannot be transferred between workers.
+
+## Other APIs
+
+- [Blob](https://developer.mozilla.org/en-US/docs/Web/API/Blob)
+- [Console](https://developer.mozilla.org/en-US/docs/Web/API/Console)
+- [FormData](https://developer.mozilla.org/en-US/docs/Web/API/FormData)
+- [Performance](https://developer.mozilla.org/en-US/docs/Web/API/Performance)
+- [setTimeout, setInterval, clearInterval](https://developer.mozilla.org/en-US/docs/Web/API/setTimeout)
+- [Streams API](https://developer.mozilla.org/en-US/docs/Web/API/Streams_API)
+- [URL](https://developer.mozilla.org/en-US/docs/Web/API/URL)
+- [URLSearchParams](https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams)
+- [WebSocket](https://developer.mozilla.org/en-US/docs/Web/API/WebSocket)
+
+---
+
+## Typings
+
+The TypeScript definitions for the implemented web APIs can be found in the
+[`lib.deno.shared_globals.d.ts`](https://github.com/denoland/deno/blob/$CLI_VERSION/cli/dts/lib.deno.shared_globals.d.ts)
+and
+[`lib.deno.window.d.ts`](https://github.com/denoland/deno/blob/$CLI_VERSION/cli/dts/lib.deno.window.d.ts)
+files.
+
+Definitions that are specific to workers can be found in the
+[`lib.deno.worker.d.ts`](https://github.com/denoland/deno/blob/$CLI_VERSION/cli/dts/lib.deno.worker.d.ts)
+file.

docs/toc.json

@@ -22,6 +22,7 @@
       "program_lifecycle": "Program lifecycle",
       "permission_apis": "Permission APIs",
       "compiler_apis": "Compiler APIs",
+      "web_platform_apis": "Web Platform APIs",
       "workers": "Workers"
     }
   },