code: def message_stanza_handler(stanza_type = None, payload_class = None,
                          payload_key = None, usage_restriction = "post-auth"):
      
      if stanza_type is None:
          stanza_type = "normal"
      return _stanza_handler("message", stanza_type, payload_class, payload_key,
                                                              usage_restriction)
docs: Method decorator generator for decorating <message/>
      stanza handler methods in `XMPPFeatureHandler` subclasses.
  
      :Parameters:
          - `payload_class`: payload class expected
          - `stanza_type`: expected value of the 'type' attribute of the stanza.
            `None` means all types except 'error'
          - `payload_key`: payload class specific filtering key
          - `usage_restriction`: optional usage restriction: "pre-auth" or
            "post-auth"
      :Types:
          - `payload_class`: subclass of `StanzaPayload`
          - `stanza_type`: `unicode`
          - `usage_restriction`: `unicode`