def provide_handler(handler, adapts=None):
    """Register a handler

        Handlers are subscription adapter factories that don't produce
        anything.  They do all of their work when called.  Handlers
        are typically used to handle events.

        If the handler has an adapts declaration, then the adapts
        argument can be omitted and the declaration will be used.  (An
        adapts argument can be provided to override the declaration.)

        CAUTION: This API should only be used from test or
        application-setup code. This API shouldn't be used by regular
        library modules, as component registration is a configuration
        activity.
        """
