content/README.md - chromium/src - Git at Google

 # Content module

 ## High-level overview
 The "content" module is located in `src/content`, and is the core code needed to
 render a page using a multi-process sandboxed browser. It includes all the web
 platform features (i.e. HTML5) and GPU acceleration. It does not include Chrome
 features, e.g. extensions/autofill/spelling etc.

 ## Motivation
 As the Chromium code has grown, features inevitably hooked into the wrong
 places, causing layering violations and dependencies that shouldn't exist. It's
 been hard for developers to figure out what the "best" way is because the APIs
 (when they existed) and features were together in the same directory. To avoid
 this happening, and to add a clear separation between the core pieces of the
 code that render a page using a multi-process browser, consensus was reached to
 move the core Chrome code into `src/content` ([content not
 chrome](http://blog.chromium.org/2008/10/content-not-chrome.html) :) ).

 ## content vs chrome
 `content` should only contain code that is required to implement the web
 platform. Generally, a feature belongs in this category if and only if all of
 the following are true:

 - Its launch is tracked on the <https://chromestatus.com/> dashboard.
 - It has an associated spec.
 - It is going through the [feature development
   lifecycle](https://www.chromium.org/blink/launching-features).

 In contrast, many features that are common to modern web browsers do not satisfy
 these criteria and thus, are not implemented in `content`. A non-exhaustive
 list:

 - Extensions
 - NaCl
 - SpellCheck
 - Autofill
 - Sync
 - Safe Browsing
 - Translate

 Instead, these features are implemented in `chrome`, while `content` only
 provides generic extension points that allow these features to subscribe to the
 events they require. Some features will require adding new extension points: for
 more information, see [How to Add New Features (without bloating
 RenderView/RenderViewHost/WebContents)](https://www.chromium.org/developers/design-documents/multi-process-architecture/how-to-add-new-features).

 Finally, there are a number of browser features that require interaction with
 online services supplied by the vendor, e.g. from the above list, Safe Browsing,
 Translate, Sync, and Autofill all require various network services to function.
 The `chrome` layer is the natural place to encapsulate that vendor-specific
 integration behavior. For the rare cases where a web platform feature
 implemented in `content` has a dependency on a network service (e.g. the network
 location service used by Geolocation), `content` should provide a way for the
 embedder to inject an endpoint (e.g. `chrome` might provide the service URL to
 use). The `content` module itself must remain generic, with no hardcoded
 vendor-specific logic.

 ## Architectural Diagram
 TODO: Draw a modern diagram.

 See an older diagram at: https://www.chromium.org/developers/content-module.

 The diagram illustrates the layering of the different modules. A module can
 include code directly from lower modules. However, a module can not include code
 from a module that is higher than it.  This is enforced through DEPS rules.
 Modules can implement embedder APIs so that modules lower than them can call
 them. Examples of these APIs are the WebKit API and the Content API.

 ## Content API
 The [Content API](public/README.md) is how code in content can indirectly call
 Chrome. Where possible, Chrome features try to hook in by filtering IPCs and
 listening to events per [How to Add New Features (without bloating
 RenderView/RenderViewHost/WebContents)](https://www.chromium.org/developers/design-documents/multi-process-architecture/how-to-add-new-features).
 When there isn't enough context (i.e.  callback from WebKit) or when the
 callback is a one-off, we have a `ContentClient` interface that the embedder
 (Chrome) implements. `ContentClient` is available in all processes. Some
 processes also have their own callback API as well, i.e.
 `ContentBrowserClient/ContentRendererClient/ContentPluginClient`.

 ## Status and Roadmap
 The current status is `content` doesn't depend on chrome at all (see the meta
 [bug](https://bugs.chromium.org/p/chromium/issues/detail?id=76697) and all bugs
 it depends on). We now have a basic browser built on top of `content`
 ("`content_shell`") that renders pages using `content` on all platforms. This
 allow developers working on the web platform and core code to only have to
 build/test content, instead of all of chrome.

 We have a separate target for `content`'s unit tests in `content_unittests`, and
 integration tests in `content_browsertests`.

 `content` is build at a separate dll to speed up the build.

 We've created an API around `content`, similar to our WebKit API. This isolates
 embedders from content's inner workings, and makes it clear to people working on
 content which methods are used by embedders.

 ## Further documentation

 * [Bluetooth](browser/bluetooth/README.md)
	# Content module

	## High-level overview
	The "content" module is located in `src/content`, and is the core code needed to
	render a page using a multi-process sandboxed browser. It includes all the web
	platform features (i.e. HTML5) and GPU acceleration. It does not include Chrome
	features, e.g. extensions/autofill/spelling etc.

	## Motivation
	As the Chromium code has grown, features inevitably hooked into the wrong
	places, causing layering violations and dependencies that shouldn't exist. It's
	been hard for developers to figure out what the "best" way is because the APIs
	(when they existed) and features were together in the same directory. To avoid
	this happening, and to add a clear separation between the core pieces of the
	code that render a page using a multi-process browser, consensus was reached to
	move the core Chrome code into `src/content` ([content not
	chrome](http://blog.chromium.org/2008/10/content-not-chrome.html) :) ).

	## content vs chrome
	`content` should only contain code that is required to implement the web
	platform. Generally, a feature belongs in this category if and only if all of
	the following are true:

	- Its launch is tracked on the <https://chromestatus.com/> dashboard.
	- It has an associated spec.
	- It is going through the [feature development
	lifecycle](https://www.chromium.org/blink/launching-features).

	In contrast, many features that are common to modern web browsers do not satisfy
	these criteria and thus, are not implemented in `content`. A non-exhaustive
	list:

	- Extensions
	- NaCl
	- SpellCheck
	- Autofill
	- Sync
	- Safe Browsing
	- Translate

	Instead, these features are implemented in `chrome`, while `content` only
	provides generic extension points that allow these features to subscribe to the
	events they require. Some features will require adding new extension points: for
	more information, see [How to Add New Features (without bloating
	RenderView/RenderViewHost/WebContents)](https://www.chromium.org/developers/design-documents/multi-process-architecture/how-to-add-new-features).

	Finally, there are a number of browser features that require interaction with
	online services supplied by the vendor, e.g. from the above list, Safe Browsing,
	Translate, Sync, and Autofill all require various network services to function.
	The `chrome` layer is the natural place to encapsulate that vendor-specific
	integration behavior. For the rare cases where a web platform feature
	implemented in `content` has a dependency on a network service (e.g. the network
	location service used by Geolocation), `content` should provide a way for the
	embedder to inject an endpoint (e.g. `chrome` might provide the service URL to
	use). The `content` module itself must remain generic, with no hardcoded
	vendor-specific logic.

	## Architectural Diagram
	TODO: Draw a modern diagram.

	See an older diagram at: https://www.chromium.org/developers/content-module.

	The diagram illustrates the layering of the different modules. A module can
	include code directly from lower modules. However, a module can not include code
	from a module that is higher than it. This is enforced through DEPS rules.
	Modules can implement embedder APIs so that modules lower than them can call
	them. Examples of these APIs are the WebKit API and the Content API.

	## Content API
	The [Content API](public/README.md) is how code in content can indirectly call
	Chrome. Where possible, Chrome features try to hook in by filtering IPCs and
	listening to events per [How to Add New Features (without bloating
	RenderView/RenderViewHost/WebContents)](https://www.chromium.org/developers/design-documents/multi-process-architecture/how-to-add-new-features).
	When there isn't enough context (i.e. callback from WebKit) or when the
	callback is a one-off, we have a `ContentClient` interface that the embedder
	(Chrome) implements. `ContentClient` is available in all processes. Some
	processes also have their own callback API as well, i.e.
	`ContentBrowserClient/ContentRendererClient/ContentPluginClient`.

	## Status and Roadmap
	The current status is `content` doesn't depend on chrome at all (see the meta
	[bug](https://bugs.chromium.org/p/chromium/issues/detail?id=76697) and all bugs
	it depends on). We now have a basic browser built on top of `content`
	("`content_shell`") that renders pages using `content` on all platforms. This
	allow developers working on the web platform and core code to only have to
	build/test content, instead of all of chrome.

	We have a separate target for `content`'s unit tests in `content_unittests`, and
	integration tests in `content_browsertests`.

	`content` is build at a separate dll to speed up the build.

	We've created an API around `content`, similar to our WebKit API. This isolates
	embedders from content's inner workings, and makes it clear to people working on
	content which methods are used by embedders.

	## Further documentation

	* [Bluetooth](browser/bluetooth/README.md)