code: def register(self, key_or_tag, obj):
          
          if key_or_tag == "default_decoder":
              self.options["default_decoder"] = obj
          else:
              self.decoders[key_or_tag] = obj
docs: Register a custom Transit tag and new parsing function with the
          decoder.  Also, you can optionally set the 'default_decoder' with
          this function.  Your new tag and parse/decode function will be added
          to the interal dictionary of decoders for this Decoder object.