docs: def keyframe(self, keyframe):
          """Set keyframe."""
          if self._keyframe == keyframe:
              return
          if self._keyframe is not None:
              raise RuntimeError('cannot reset keyframe')
          if len(self._offsetscounts[0]) != len(keyframe.dataoffsets):
              raise RuntimeError('incompatible keyframe')
          if keyframe.is_tiled:
              pass
          if keyframe.is_contiguous:
              self._offsetscounts = ([self._offsetscounts[0][0]],
                                     [keyframe.is_contiguous[1]])
          else:
              self._offsetscounts = clean_offsetscounts(*self._offsetscounts)
          self._keyframe = keyframe