'Add a :class:`~matplotlib.container.Container` instance
to the axes.
Returns the collection.'

def add_container(self, container):

    label = container.get_label()
    if (not label):
        container.set_label((u'_container%d' % len(self.containers)))
    self.containers.append(container)
    container.set_remove_method((lambda h: self.containers.remove(h)))
    return container
