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+Extending BE
+============
+
+Adding commands
+---------------
+
+To write a plugin, you simply create a new file in the
+``libbe/commands/`` directory.  Take a look at one of the simpler
+plugins (e.g. ``remove.py``) for an example of how that looks, and to
+start getting a feel for the libbe interface.
+
+See ``libbe/commands/base.py`` for the definition of the important
+classes ``Option``, ``Argument``, ``Command``, ``InputOutput``,
+``StorageCallbacks``, and ``UserInterface`` classes.  You'll be
+subclassing ``Command`` for your command, but all those classes will
+be important.
+
+
+Command completion
+~~~~~~~~~~~~~~~~~~
+
+BE implements a general framework to make it easy to support command
+completion for arbitrary plugins.  In order to support this system,
+any of your completable ``Argument()`` instances (in your command's
+``.options`` or ``.args``) should be initialized with some valid
+completion_callback function.  Some common cases are defined in
+``libbe.command.util``.  If you need more flexibility, see
+``libbe.command.list``'s ``--sort`` option for an example of
+extensions via ``libbe.command.util.Completer``, or write a custom
+completion function from scratch.
+
+
+Adding user interfaces
+----------------------
+
+Take a look at ``libbe/ui/command_line.py`` for an example.  Basically
+you'll need to setup a ``UserInterface`` instance for running commands.
+More details to come after I write an HTML UI...
+
+
+Testing
+=======
+
+Run any tests in your module with::
+
+    be$ python test.py <python.module.name>
+
+for example:
+
+    be$ python test.py libbe.command.merge
+
+For a definition of "any tests", see ``test.py``'s
+``add_module_tests()`` function.
+
+Note that you will need to run ``make`` before testing a clean BE
+branch to auto-generate required files like ``libbe/_version.py``.
+
+
+Profiling
+=========
+
+Find out which 20 calls take the most cumulative time (time of
+execution + childrens' times)::
+
+    $ python -m cProfile -o profile be [command] [args]
+    $ python -c "import pstats; p=pstats.Stats('profile'); p.sort_stats('cumulative').print_stats(20)"
+
+It's often useful to toss::
+
+    import sys, traceback
+    print >> sys.stderr, '-'*60, '\n', '\n'.join(traceback.format_stack()[-10:])
+
+into expensive functions (e.g. ``libbe.util.subproc.invoke()``) if
+you're not sure why they're being called.