code: def from_etree(cls, etree_element):
          
          ins = SaltElement.from_etree(etree_element)
          # TODO: this looks dangerous, ask Stackoverflow about it!
          ins.__class__ = SaltNode.mro()[0]  # convert SaltElement into SaltNode
          ins.layers = get_layer_ids(etree_element)
          ins.features = get_annotations(etree_element)
          return ins
docs: creates a ``SaltNode`` instance from the etree representation of an
          <nodes> element from a SaltXMI file.