'Queues a message to be stored.
The message is only queued if it contained something and its level is
not less than the recording level (``self.level``).'

def add(self, level, message, extra_tags=''):

    if (not message):
        return
    level = int(level)
    if (level < self.level):
        return
    self.added_new = True
    message = Message(level, message, extra_tags=extra_tags)
    self._queued_messages.append(message)
