'set the bbox that the child will be anchored.
*bbox* can be a Bbox instance, a list of [left, bottom, width,
height], or a list of [left, bottom] where the width and
height will be assumed to be zero. The bbox will be
transformed to display coordinate by the given transform.'

def set_bbox_to_anchor(self, bbox, transform=None):

    if ((bbox is None) or isinstance(bbox, BboxBase)):
        self._bbox_to_anchor = bbox
    else:
        try:
            l = len(bbox)
        except TypeError:
            raise ValueError((u'Invalid    argument    for    bbox    :    %s' % str(bbox)))
        if (l == 2):
            bbox = [bbox[0], bbox[1], 0, 0]
        self._bbox_to_anchor = Bbox.from_bounds(*bbox)
    self._bbox_to_anchor_transform = transform
    self.stale = True
