+The C<MR_CONFIG> environment variable is set to the .mrconfig file
+that defines the repo being acted on, or, if the repo is not yet in a config
+file, the F<.mrconfig> file that should be modified to register the repo.
+
+The C<MR_ACTION> environment variable is set to the command being run
+(update, checkout, etc).
+
+A few parameters have special meanings:
+
+=over 4
+
+=item skip
+
+If the "skip" parameter is set and its command returns true, then B<mr>
+will skip acting on that repository. The command is passed the action
+name in C<$1>.
+
+Here are two examples. The first skips the repo unless
+mr is run by joey. The second uses the hours_since function
+(included in mr's built-in library) to skip updating the repo unless it's
+been at least 12 hours since the last update.
+
+ [mystuff]
+ checkout = ...
+ skip = test `whoami` != joey
+
+ [linux]
+ checkout = ...
+ skip = [ "$1" = update ] && ! hours_since "$1" 12
+
+Another way to use skip is for a lazy checkout. This makes mr skip
+operating on a repo unless it already exists. To enable the
+repo, you have to explicitly check it out (using "mr --force -d foo checkout").
+
+ [foo]
+ checkout = ...
+ skip = lazy
+
+=item order
+
+The "order" parameter can be used to override the default ordering of
+repositories. The default order value is 10. Use smaller values to make
+repositories be processed earlier, and larger values to make repositories
+be processed later.
+
+Note that if a repository is located in a subdirectory of another
+repository, ordering it to be processed earlier is not recommended.
+
+=item chain
+
+If the "chain" parameter is set and its command returns true, then B<mr>
+will try to load a F<.mrconfig> file from the root of the repository.
+
+=item include
+
+If the "include" parameter is set, its command is ran, and should output
+additional mrconfig file content. The content is included as if it were
+part of the including file.
+
+Unlike all other parameters, this parameter does not need to be placed
+within a section.
+
+B<mr> ships several libraries that can be included to add support for
+additional version control type things (unison, git-svn, vcsh, git-fake-bare,
+git-subtree). To include them all, you could use:
+
+ include = cat /usr/share/mr/*
+
+See the individual files for details.
+
+=item deleted
+
+If the "deleted" parameter is set and its command returns true, then
+B<mr> will treat the repository as deleted. It won't ever actually delete
+the repository, but it will warn if it sees the repository's directory.
+This is useful when one mrconfig file is shared among multiple machines,
+to keep track of and remember to delete old repositories.
+
+=item lib
+
+The "lib" parameter can specify some shell code that will be run
+before each command, this can be a useful way to define shell
+functions for other commands to use.
+
+Unlike most other parameters, this can be specified multiple times, in
+which case the chunks of shell code are accumulatively concatenated
+together.
+
+=item fixups
+
+If the "fixups" parameter is set, its command is run whenever a repository
+is checked out, or updated. This provides an easy way to do things
+like permissions fixups, or other tweaks to the repository content,
+whenever the repository is changed.
+
+=item VCS_action
+
+When looking for a command to run for a given action, mr first looks for
+a parameter with the same name as the action. If that is not found, it
+looks for a parameter named "VCS_action" (substituting in the name of the
+version control system and the action).
+
+Internally, mr has settings for "git_update", "svn_update", etc. To change
+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.