Convenience method to add multiple frames at once.

def add_children(self, frames, after=None):
        '''
        Convenience method to add multiple frames at once.
        '''
        if after is not None:
            # if there's an 'after' parameter, add the frames in reverse so the order is
            # preserved.
            for frame in reversed(frames):
                self.add_child(frame, after=after)
        else:
            for frame in frames:
                self.add_child(frame)