'Display to the user a message sent to this group from the given sender.
@param sender: The person sending the message.
@type sender: C{str}
@param text: The sent message.
@type text: C{str}
@param metadata: Metadata associated with this message.
@type metadata: C{dict}'

def showGroupMessage(self, sender, text, metadata=None):

    raise NotImplementedError('Subclasses    must    implement    this    method')
