+FILTER API
+----------
+about filter::
+ This filter is given a single parameter: the filename of the source
+ file to filter. The filter can use the filename to determine (for
+ example) the type of syntax to follow when formatting the readme file.
+ The about text that is to be filtered is available on standard input
+ and the filtered text is expected on standard output.
+
+commit filter::
+ This filter is given no arguments. The commit message text that is to
+ be filtered is available on standard input and the filtered text is
+ expected on standard output.
+
+source filter::
+ This filter is given a single parameter: the filename of the source
+ file to filter. The filter can use the filename to determine (for
+ example) the syntax highlighting mode. The contents of the source
+ file that is to be filtered is available on standard input and the
+ filtered contents is expected on standard output.
+
+Also, all filters are handed the following environment variables:
+
+- CGIT_REPO_URL (from repo.url)
+- CGIT_REPO_NAME (from repo.name)
+- CGIT_REPO_PATH (from repo.path)
+- CGIT_REPO_OWNER (from repo.owner)
+- CGIT_REPO_DEFBRANCH (from repo.defbranch)
+- CGIT_REPO_SECTION (from repo.section)
+- CGIT_REPO_CLONE_URL (from repo.clone-url)
+
+If a setting is not defined for a repository and the corresponding global
+setting is also not defined (if applicable), then the corresponding
+environment variable will be unset.
+
+
+MACRO EXPANSION
+---------------
+The following cgitrc options supports a simple macro expansion feature,
+where tokens prefixed with "$" are replaced with the value of a similary
+named environment variable:
+
+- cache-root
+- include
+- project-list
+- scan-path
+
+Macro expansion will also happen on the content of $CGIT_CONFIG, if
+defined.
+
+One usage of this feature is virtual hosting, which in its simplest form
+can be accomplished by adding the following line to /etc/cgitrc:
+
+ include=/etc/cgitrc.d/$HTTP_HOST
+
+The following options are expanded during request processing, and support
+the environment variables defined in "FILTER API":
+
+- clone-url
+- repo.clone-url
+
+