A mode for a multimode menu item, containing information about when
the mode is active and what the parameter means when it is active.
:param title: The key in the language map for the title used by the
MultiModeMenu when in this mode.
:param available_when: Markdown fragment describing when this menu item is
available.
:param description: Path to the description of this mode, relative to
``docs/menu``
:param name: The key in the language map used to describe this menu item
when presenting a submenu. A value of None (the default) causes this to
default to the same value as ``title``