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+:mod:`packaging.command` --- Standard Packaging commands
+========================================================
+
+.. module:: packaging.command
+   :synopsis: Standard packaging commands.
+
+
+This subpackage contains one module for each standard Packaging command, such as
+:command:`build`  or :command:`upload`.  Each command is implemented as a
+separate module, with the command name as the name of the module and of the
+class defined therein.
+
+
+
+:mod:`packaging.command.cmd` --- Abstract base class for Packaging commands
+===========================================================================
+
+.. module:: packaging.command.cmd
+   :synopsis: Abstract base class for commands.
+
+
+This module supplies the abstract base class :class:`Command`.  This class is
+subclassed by the modules in the packaging.command subpackage.
+
+
+.. class:: Command(dist)
+
+   Abstract base class for defining command classes, the "worker bees" of the
+   Packaging.  A useful analogy for command classes is to think of them as
+   subroutines with local variables called *options*.  The options are declared
+   in :meth:`initialize_options` and defined (given their final values) in
+   :meth:`finalize_options`, both of which must be defined by every command
+   class.  The distinction between the two is necessary because option values
+   might come from the outside world (command line, config file, ...), and any
+   options dependent on other options must be computed after these outside
+   influences have been processed --- hence :meth:`finalize_options`.  The body
+   of the subroutine, where it does all its work based on the values of its
+   options, is the :meth:`run` method, which must also be implemented by every
+   command class.
+
+   The class constructor takes a single argument *dist*, a
+   :class:`~packaging.dist.Distribution` instance.
+
+
+Creating a new Packaging command
+--------------------------------
+
+This section outlines the steps to create a new Packaging command.
+
+.. XXX the following paragraph is focused on the stdlib; expand it to document
+   how to write and register a command in third-party projects
+
+A new command lives in a module in the :mod:`packaging.command` package. There
+is a sample template in that directory called :file:`command_template`.  Copy
+this file to a new module with the same name as the new command you're
+implementing.  This module should implement a class with the same name as the
+module (and the command).  So, for instance, to create the command
+``peel_banana`` (so that users can run ``setup.py peel_banana``), you'd copy
+:file:`command_template` to :file:`packaging/command/peel_banana.py`, then edit
+it so that it's implementing the class :class:`peel_banana`, a subclass of
+:class:`Command`.  It must define the following methods:
+
+.. method:: Command.initialize_options()
+
+   Set default values for all the options that this command supports.  Note that
+   these defaults may be overridden by other commands, by the setup script, by
+   config files, or by the command line.  Thus, this is not the place to code
+   dependencies between options; generally, :meth:`initialize_options`
+   implementations are just a bunch of ``self.foo = None`` assignments.
+
+
+.. method:: Command.finalize_options()
+
+   Set final values for all the options that this command supports. This is
+   always called as late as possible, i.e. after any option assignments from the
+   command line or from other commands have been done.  Thus, this is the place
+   to to code option dependencies: if *foo* depends on *bar*, then it is safe to
+   set *foo* from *bar* as long as *foo* still has the same value it was
+   assigned in :meth:`initialize_options`.
+
+
+.. method:: Command.run()
+
+   A command's raison d'etre: carry out the action it exists to perform,
+   controlled by the options initialized in :meth:`initialize_options`,
+   customized by other commands, the setup script, the command line, and config
+   files, and finalized in :meth:`finalize_options`.  All terminal output and
+   filesystem interaction should be done by :meth:`run`.
+
+
+Command classes may define this attribute:
+
+
+.. attribute:: Command.sub_commands
+
+   *sub_commands* formalizes the notion of a "family" of commands,
+   e.g. ``install_dist`` as the parent with sub-commands ``install_lib``,
+   ``install_headers``, etc.  The parent of a family of commands defines
+   *sub_commands* as a class attribute; it's a list of 2-tuples ``(command_name,
+   predicate)``, with *command_name* a string and *predicate* a function, a
+   string or ``None``.  *predicate* is a method of the parent command that
+   determines whether the corresponding command is applicable in the current
+   situation.  (E.g. ``install_headers`` is only applicable if we have any C
+   header files to install.)  If *predicate* is ``None``, that command is always
+   applicable.
+
+   *sub_commands* is usually defined at the *end* of a class, because
+   predicates can be methods of the class, so they must already have been
+   defined.  The canonical example is the :command:`install_dist` command.
+
+.. XXX document how to add a custom command to another one's subcommands