'Add any :class:`~matplotlib.artist.Artist` to the container box'

def add_artist(self, a):

    self._children.append(a)
    if (not a.is_transform_set()):
        a.set_transform(self.get_transform())
    if (self.axes is not None):
        a.axes = self.axes
    fig = self.figure
    if (fig is not None):
        a.set_figure(fig)
