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+Chrome Registration
+-------------------
+
+What is chrome?
+---------------
+
+`Chrome` is the set of user interface elements of the
+application window that are outside the window's content area. Toolbars,
+menu bars, progress bars, and window title bars are all examples of
+elements that are typically part of the chrome.
+
+``chrome.manifest`` files are used to register XPCOM components and sources for the chrome protocol.
+Every application supplies a root ``chrome.manifest`` file that Mozilla reads on startup.
+
+Chrome providers
+----------------
+
+A supplier of chrome for a given window type (e.g., for the browser
+window) is called a chrome provider. The providers work together to
+supply a complete set of chrome for a particular window, from the images
+on the toolbar buttons to the files that describe the text, content, and
+appearance of the window itself.
+
+There are three basic types of chrome providers:
+
+Content
+ The main source file for a window description comes from the content
+ provider, and it can be any file type viewable from within Mozilla.
+ It will typically be a XUL file, since XUL is designed for describing
+ the contents of windows and dialogs. The JavaScript files that define
+ the user interface are also contained within the content packages.
+
+Locale
+ Localizable applications keep all their localized information in
+ locale providers and Fluent FTL files, which are handled separately.
+ This allows translators to plug in a different
+ chrome package to translate an application without altering the rest
+ of the source code. In a chrome provider, localizable files are mostly
+ Java-style properties files.
+Skin
+ A skin provider is responsible for providing a complete set of files
+ that describe the visual appearance of the chrome. Typically a skin
+ provider will provide CSS files and
+ images.
+
+The chrome registry
+-------------------
+
+The Gecko runtime maintains a service known as the chrome registry that
+provides mappings from chrome package names to the physical location of
+chrome packages on disk.
+
+This chrome registry is configurable and persistent, and thus a user can
+install different chrome providers, and select a preferred skin and
+locale. This is accomplished through xpinstall and the extension
+manager.
+
+In order to inform the chrome registry of the available chrome, a text
+manifest is used: this manifest is "chrome.manifest" in the root of an
+extension, or theme, or XULRunner application.
+
+The plaintext chrome manifests are in a simple line-based format. Each
+line is parsed individually; if the line is parsable the chrome registry
+takes the action identified by that line, otherwise the chrome registry
+ignores that line (and prints a warning message in the runtime error
+console).
+
+.. code::
+
+ locale packagename localename path/to/files
+ skin packagename skinname path/to/files
+
+.. note::
+
+ The characters @ # ; : ? / are not allowed in the
+ packagename.
+
+Manifest instructions
+---------------------
+
+comments
+~~~~~~~~
+
+.. code::
+
+ # this line is a comment - you can put here whatever you want
+
+A line is a comment if it begins with the character '#'. Any following
+character in the same line is ignored.
+
+manifest
+~~~~~~~~
+
+::
+
+ manifest subdirectory/foo.manifest [flags]
+
+This will load a secondary manifest file. This can be useful for
+separating component and chrome registration instructions, or separate
+platform-specific registration data.
+
+component
+~~~~~~~~~
+
+::
+
+ component {00000000-0000-0000-0000-000000000000} components/mycomponent.js [flags]
+
+Informs Mozilla about a component CID implemented by an XPCOM component
+implemented in JavaScript (or another scripting language, if
+applicable). The ClassID {0000...} must match the ClassID implemented by
+the component. To generate a unique ClassID, use a UUID generator
+program or site.
+
+contract
+~~~~~~~~
+
+::
+
+ contract @foobar/mycontract;1 {00000000-0000-0000-0000-000000000000} [flags]
+
+Maps a contract ID (a readable string) to the ClassID for a specific
+implementation. Typically a contract ID will be paired with a component
+entry immediately preceding.
+
+category
+~~~~~~~~
+
+::
+
+ category category entry-name value [flags]
+
+Registers an entry in the `category manager`. The
+specific format and meaning of category entries depend on the category.
+
+content
+~~~~~~~
+
+A content package is registered with the line:
+
+::
+
+ content packagename uri/to/files/ [flags]
+
+This will register a location to use when resolving the URI
+``chrome://packagename/content/...``. The URI may be absolute or
+relative to the location of the manifest file. Note: it must end with a
+'/'.
+
+locale
+~~~~~~
+
+A locale package is registered with the line:
+
+.. code::
+
+ locale packagename localename uri/to/files/ [flags]
+
+This will register a locale package when resolving the URI
+chrome://*packagename*/locale/... . The *localename* is usually a plain
+language identifier "en" or a language-country identifier "en-US". If
+more than one locale is registered for a package, the chrome registry
+will select the best-fit locale using the user's preferences.
+
+skin
+~~~~
+
+A skin package is registered with the line:
+
+.. code::
+
+ skin packagename skinname uri/to/files/ [flags]
+
+This will register a skin package when resolving the URI
+chrome://packagename/skin/... . The *skinname* is an opaque string
+identifying an installed skin. If more than one skin is registered for a
+package, the chrome registry will select the best-fit skin using the
+user's preferences.
+
+style
+~~~~~
+
+Style overlays (custom CSS which will be applied to a chrome page) are
+registered with the following syntax:
+
+.. code::
+
+ style chrome://URI-to-style chrome://stylesheet-URI [flags]
+
+override
+~~~~~~~~
+
+In some cases an extension or embedder may wish to override a chrome
+file provided by the application or XULRunner. In order to allow for
+this, the chrome registration manifest allows for "override"
+instructions:
+
+.. code::
+
+ override chrome://package/type/original-uri.whatever new-resolved-URI [flags]
+
+Note: overrides are not recursive (so overriding
+chrome://foo/content/bar/ with file:///home/john/blah/ will not usually
+do what you want or expect it to do). Also, the path inside overridden
+files is relative to the overridden path, not the original one (this can
+be annoying and/or useful in CSS files, for example).
+
+resource
+~~~~~~~~
+
+Aliases can be created using the ``resource`` instruction:
+
+.. code::
+
+ resource aliasname uri/to/files/ [flags]
+
+This will create a mapping for ``resource://<aliasname>/`` URIs to the
+path given.
+
+.. note::
+
+ **Note:** There are no security restrictions preventing web content
+ from including content at resource: URIs, so take care what you make
+ visible there.
+
+Manifest flags
+--------------
+
+Manifest lines can have multiple, space-delimited flags added at the end
+of the registration line. These flags mark special attributes of chrome
+in that package, or limit the conditions under which the line is used.
+
+application
+~~~~~~~~~~~
+
+Extensions may install into multiple applications. There may be chrome
+registration lines which only apply to one particular application. The
+flag
+
+.. code::
+
+ application=app-ID
+
+indicates that the instruction should only be applied if the extension
+is installed into the application identified by *app-ID*. Multiple
+application flags may be included on a single line, in which case the
+line is applied if any of the flags match.
+
+This example shows how a different overlay can be used for different
+applications:
+
+::
+
+ overlay chrome://browser/content/browser.xul chrome://myaddon/content/ffOverlay.xul application={ec8030f7-c20a-464f-9b0e-13a3a9e97384}
+ overlay chrome://messenger/content/mailWindowOverlay.xul chrome://myaddon/content/tbOverlay.xul application={3550f703-e582-4d05-9a08-453d09bdfdc6}
+ overlay chrome://songbird/content/xul/layoutBaseOverlay.xul chrome://myaddon/content/sbOverlay.xul application=songbird@songbirdnest.com
+
+appversion
+~~~~~~~~~~
+
+Extensions may install into multiple versions of an application. There
+may be chrome registration lines which only apply to a particular
+application version. The flag
+
+.. code::
+
+ appversion=version
+ appversion<version
+ appversion<=version
+ appversion>version
+ appversion>=version
+
+indicates that the instruction should only be applied if the extension
+is installed into the application version identified. Multiple
+``appversion`` flags may be included on a single line, in which case the
+line is applied if any of the flags match. The version string must
+conform to the `Toolkit version format`.
+
+platformversion
+~~~~~~~~~~~~~~~
+
+When supporting more then one application, it is often more convenient
+for an extension to specify which Gecko version it is compatible with.
+This is particularly true for binary components. If there are chrome
+registration lines which only apply to a particular Gecko version, the
+flag
+
+.. code::
+
+ platformversion=version
+ platformversion<version
+ platformversion<=version
+ platformversion>version
+ platformversion>=version
+
+indicates that the instruction should only be applied if the extension
+is installed into an application using the Gecko version identified.
+Multiple ``platformversion`` flags may be included on a single line, in
+which case the line is applied if any of the flags match.
+
+contentaccessible
+~~~~~~~~~~~~~~~~~
+
+Chrome resources can no longer be referenced from within <img>,
+<script>, or other elements contained in, or added to, content that was
+loaded from an untrusted source. This restriction applies to both
+elements defined by the untrusted source and to elements added by
+trusted extensions. If such references need to be explicitly allowed,
+set the ``contentaccessible`` flag to ``yes`` to obtain the behavior
+found in older versions of Firefox. See
+`bug 436989 <https://bugzilla.mozilla.org/show_bug.cgi?id=436989>`__.
+
+The ``contentaccessible`` flag applies only to content packages: it is
+not recognized for locale or skin registration. However, the matching
+locale and skin packages will also be exposed to content.
+
+**n.b.:** Because older versions of Firefox do not understand the
+``contentaccessible`` flag, any extension designed to work with both
+Firefox 3 and older versions of Firefox will need to provide a fallback.
+For example:
+
+::
+
+ content packagename chrome/path/
+ content packagename chrome/path/ contentaccessible=yes
+
+os
+~~
+
+Extensions (or themes) may offer different features depending on the
+operating system on which Firefox is running. The value is compared to
+the value of `OS_TARGET` for the platform.
+
+.. code::
+
+ os=WINNT
+ os=Darwin
+
+osversion
+~~~~~~~~~
+
+An extension or theme may need to operate differently depending on which
+version of an operating system is running. For example, a theme may wish
+to adopt a different look on Mac OS X 10.5 than 10.4:
+
+.. code::
+
+ osversion>=10.5
+
+abi
+~~~
+
+If a component is only compatible with a particular ABI, it can specify
+which ABI/OS by using this directive. The value is taken from the
+`nsIXULRuntime` OS and
+XPCOMABI values (concatenated with an underscore). For example:
+
+::
+
+ binary-component component/myLib.dll abi=WINNT_x86-MSVC
+ binary-component component/myLib.so abi=Linux_x86-gcc3
+
+platform (Platform-specific packages)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Some packages are marked with a special flag indicating that they are
+platform specific. Some parts of content, skin, and locales may be
+different based on the platform being run. These packages contain three
+different sets of files, for Windows and OS/2, Macintosh, and Unix-like
+platforms. For example, the order of the "OK" and "Cancel" buttons in a
+dialog is different, as well as the names of some items.
+
+The "platform" modifier is only parsed for content registration; it is
+not recognized for locale or skin registration. However, it applies to
+content, locale, and skin parts of the package, when specified.
+
+process
+~~~~~~~
+
+In electrolysis registrations can be set to only apply in either the
+main process or any content processes. The "process" flag selects
+between these two. This can allow you to register different components
+for the same contract ID or ensure a component can only be loaded in the
+main process.
+
+::
+
+ component {09543782-22b1-4a0b-ba07-9134365776ee} maincomponent.js process=main
+ component {98309951-ac89-4642-afea-7b2b6216bcef} contentcomponent.js process=content
+
+remoteenabled
+~~~~~~~~~~~~~
+
+In `multiprocess Firefox`, the
+default is that a given chrome: URI will always be loaded into the
+chrome process. If you set the "remoteenabled" flag, then the page will
+be loaded in the same process as the ``browser`` that loaded it:
+
+::
+
+ content packagename chrome/path/ remoteenabled=yes
+
+remoterequired
+~~~~~~~~~~~~~~
+
+In `multiprocess Firefox`, the
+default is that a given chrome: URI will always be loaded into the
+chrome process. If you set the "remoterequired" flag, then the page will
+always be loaded into a child process:
+
+::
+
+ content packagename chrome/path/ remoterequired=yes
+
+Example chrome manifest
+-----------------------
+
+.. list-table::
+ :widths: 20 20 20 20
+
+
+ * - type
+ - engine
+ - language
+ - url
+ * - content
+ - branding
+ - browser/content/branding/
+ - contentaccessible=yes
+ * - content
+ - browser
+ - browser/content/browser/
+ - contentaccessible=yes
+ * - override
+ -
+ - chrome://global/content/license.html
+ - chrome://browser/content/license.html
+ * - resource
+ - payments
+ - browser/res/payments/
+ -
+ * - skin
+ - browser
+ - classic/1.0 browser/skin/classic/browser/
+ -
+ * - locale
+ - branding
+ - en-US
+ - en-US/locale/branding/
+ * - locale
+ - browser
+ - en-US
+ - en-US/locale/browser/
+ * - locale
+ - browser-region
+ - en-US
+ - en-US/locale/browser-region/