..note::

To register a handlerforonly a specific bus, add a ``bus`` attributehaving the

name of this bus as value to the``messenger.message_handler`` tag in thehandler's

service definition.

To register a handler onlyfora specific bus, add a ``bus`` attributeto

the handler's service tag (``messenger.message_handler``) and use thebus

name as its value.

Type-hints and Auto-wiring