parameters: (self, message_name)
docstring: Invoked at the start of a <message> with message's name.
docstring_summary: Invoked at the start of a <message> with message's name.
docstring_tokens: Invoked at the start of a <message > with message s name .
function: def __OnOpenMessage(self, message_name):
      """Invoked at the start of a <message> with message's name."""
      assert not self.__IsExtractingMessage()
      self.__message_name = (message_name if message_name in self.__id_set
                             else None)
      if self.__message_name:
        self.__characters_callback = self.__OnMessageText
function_tokens: def __OnOpenMessage ( self , message_name ) : assert not self . __IsExtractingMessage ( ) self . __message_name = ( message_name if message_name in self . __id_set else None ) if self . __message_name : self . __characters_callback = self . __OnMessageText