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+.. _jar_manifests:
+
+=============
+JAR Manifests
+=============
+
+JAR Manifests are plaintext files in the tree that are used to package chrome
+files into the correct JARs, and create
+`Chrome Registration <https://developer.mozilla.org/en-US/docs/Chrome_Registration>`_
+manifests. JAR Manifests are commonly named ``jar.mn``. They are
+declared in ``moz.build`` files using the ``JAR_MANIFESTS`` variable.
+
+``jar.mn`` files are automatically processed by the build system when building a
+source directory that contains one. The ``jar``.mn is run through the
+:ref:`preprocessor` before being passed to the manifest processor. In order to
+have ``@variables@`` expanded (such as ``@AB_CD@``) throughout the file, add
+the line ``#filter substitution`` at the top of your ``jar.mn`` file.
+
+The format of a jar.mn is fairly simple; it consists of a heading specifying
+which JAR file is being packaged, followed by indented lines listing files and
+chrome registration instructions.
+
+To see a simple ``jar.mn`` file at work, see ``toolkit/profile/jar.mn``. A much
+more complex ``jar.mn`` is at ``toolkit/locales/jar.mn``.
+
+Shipping Chrome Files
+=====================
+
+To ship chrome files in a JAR, an indented line indicates a file to be packaged::
+
+   <jarfile>.jar:
+     path/in/jar/file_name.xul     (source/tree/location/file_name.xul)
+
+The source tree location may also be an *absolute* path (taken from the
+top of the source tree::
+
+   path/in/jar/file_name.xul     (/path/in/sourcetree/file_name.xul)
+
+An asterisk marker (``*``) at the beginning of the line indicates that the
+file should be processed by the :ref:`preprocessor` before being packaged::
+
+   * path/in/jar/preprocessed.xul  (source/tree/location/file_name.xul)
+
+A plus marker (``+``) at the beginning of the line indicates that the file
+should replace an existing file, even if the source file's timestamp isn't
+newer than the existing file::
+
+   + path/in/jar/file_name.xul     (source/tree/location/my_file_name.xul)
+
+Preprocessed files always replace existing files, to ensure that changes in
+``#expand`` or ``#include`` directives are picked up, so ``+`` and ``*`` are
+equivalent.
+
+There is a special source-directory format for localized files (note the
+percent sign in the source file location): this format reads ``localized.dtd``
+from the ``en-US`` directory if building an English version, and reads the
+file from the alternate localization source tree
+``/l10n/<locale>/path/localized.dtd`` if building a localized version::
+
+   locale/path/localized.dtd     (%localized/path/localized.dtd)
+
+Register Chrome
+===============
+
+`Chrome Registration <https://developer.mozilla.org/en-US/docs/Chrome_Registration>`_
+instructions are marked with a percent sign (``%``) at the beginning of the
+line, and must be part of the definition of a JAR file. Any additional percents
+signs are replaced with an appropriate relative URL of the JAR file being
+packaged::
+
+   % content global %path/in/jar/
+   % overlay chrome://blah/content/blah.xul chrome://foo/content/overlay.xul
+
+There are two possible locations for a manifest file. If the chrome is being
+built into a standalone application, the ``jar.mn`` processor creates a
+``<jarfilename>.manifest`` next to the JAR file itself. This is the default
+behavior.
+
+If the build specifies ``USE_EXTENSION_MANIFEST = 1``, the ``jar.mn`` processor
+creates a single ``chrome.manifest`` file suitable for registering chrome as
+an extension.