+the action that is performed for a given version control system, you can
+override these VCS specific actions. To add a new version control system,
+you can just add VCS specific actions for it.
+
+=item pre_ and post_
+
+If a "pre_action" parameter is set, its command is run before mr performs the
+specified action. Similarly, "post_action" parameters are run after mr
+successfully performs the specified action. For example, "pre_commit" is
+run before committing; "post_update" is run after updating.
+
+=item _append
+
+Any parameter can be suffixed with C<_append>, to add an additional value
+to the existing value of the parameter. In this way, actions
+can be constructed accumulatively.
+
+=item VCS_test
+
+The name of the version control system is itself determined by
+running each defined "VCS_test" action, until one succeeds.
+
+=item VCS_dir_test
+
+This is a more optimised way to test for the version control system.
+Each "VCS_dir_test" action is run once, and can output lines consisting
+of the name of a VCS, and a directory to look for in the top of a repo
+to detect that VCS.
+
+=back
+
+=head1 UNTRUSTED MRCONFIG FILES
+
+Since mrconfig files can contain arbitrary shell commands, they can do
+anything. This flexibility is good, but it also allows a malicious mrconfig
+file to delete your whole home directory. Such a file might be contained
+inside a repository that your main F<~/.mrconfig> checks out. To
+avoid worries about evil commands in a mrconfig file, mr defaults to
+reading all mrconfig files other than the main F<~/.mrconfig> in untrusted
+mode. In untrusted mode, mrconfig files are limited to running only known
+safe commands (like "git clone") in a carefully checked manner.
+
+To configure mr to trust other mrconfig files, list them in F<~/.mrtrust>.
+One mrconfig file should be listed per line. Either the full pathname
+should be listed, or the pathname can start with F<~/> to specify a file
+relative to your home directory.
+
+=head1 OFFLINE LOG FILE
+
+The F<~/.mrlog> file contains commands that mr has remembered to run later,
+due to being offline. You can delete or edit this file to remove commands,
+or even to add other commands for 'mr online' to run. If the file is
+present, mr assumes it is in offline mode.
+
+=head1 EXTENSIONS
+
+mr can be extended to support things such as unison and git-svn. Some
+files providing such extensions are available in F</usr/share/mr/>. See
+the documentation in the files for details about using them.
+
+=head1 EXIT STATUS
+
+mr returns nonzero if a command failed in any of the repositories.