'set text rotation mode. If "anchor", the un-rotated text
will first aligned according to their *ha* and
*va*, and then will be rotated with the alignement
reference point as a origin. If None (default), the text will be
rotated first then will be aligned.'

def set_rotation_mode(self, m):

    if ((m is None) or (m in [u'anchor', u'default'])):
        self._rotation_mode = m
    else:
        raise ValueError((u'Unknown    rotation_mode    :    %s' % repr(m)))
    self.stale = True
