@staticmethod
def remover(fn):
    """Tag the method as the collection remover.

        The remover method is called with one positional argument: the value
        to remove. The method will be automatically decorated with
        :meth:`removes_return` if not already decorated::

            @collection.remover
            def zap(self, entity): ...

            # or, equivalently
            @collection.remover
            @collection.removes_return()
            def zap(self, ): ...

        If the value to remove is not present in the collection, you may
        raise an exception or return None to ignore the error.

        If the remove method is internally instrumented, you must also
        receive the keyword argument '_sa_initiator' and ensure its
        promulgation to collection events.

        """
    fn._sa_instrument_role = 'remover'
    return fn
