code: def stream_element_handler(element_name, usage_restriction = None):
      
      def decorator(func):
          """The decorator"""
          func._pyxmpp_stream_element_handled = element_name
          func._pyxmpp_usage_restriction = usage_restriction
          return func
      return decorator
docs: Method decorator generator for decorating stream element
      handler methods in `StreamFeatureHandler` subclasses.
  
      :Parameters:
          - `element_name`: stream element QName
          - `usage_restriction`: optional usage restriction: "initiator" or
            "receiver"
      :Types:
          - `element_name`: `unicode`
          - `usage_restriction`: `unicode`