@classmethod
def get_outdated_docs(cls, app, env, added, changed, removed):
    """Handler for Sphinx's env-get-outdated event.

        This handler gives a Sphinx extension a chance to indicate that some
        set of documents are out of date and need to be re-rendered. The
        implementation here is stupid, for now, and always says that anything
        that uses the directive needs to be re-rendered.

        We should make it smarter, at some point, and have it figure out which
        modules are used by the associated handlers, and whether they have
        actually been updated since the last time the given document was
        rendered.
        """
    state = getattr(env, cls.directive_name, None)
    if state and state.doc_names:
        return sorted(state.doc_names)
    else:
        return []
