def __call__(dirname, create=False):
    """Opens a `Maildir` folder at a given filesystem path.

        If `create` is ``True``, the folder will be created when it does not
        exist.  If `create` is ``False`` and the folder does not exist, an
        exception (``OSError``) will be raised.

        If path points to a file or an existing directory that is not a
        valid `Maildir` folder, an exception is raised regardless of the
        `create` argument.
        """
