def command(key):
    """Make a string that tmux will parse as the command key (also known as the
    meta, super, cmd, Apple, and Windows key) and ``key`` pressed at the same
    time.

    .. note::

       The ``key`` parameter is case-sensitive. If ``key`` is uppercase, it's
       equivalent to entering :kbd:`Shift` and the key.

       .. doctest::

          >>> from oraide.keys import command
          >>> command('a')  # command + a
          'M-a'
          >>> command('A')  # command + shift + a
          'M-A'
    """
    return 'M-{}'.format(key)
