code: def get_layer_ids(element):
      
      layers = []
      if element.xpath('@layers'):
          layers_string = element.xpath('@layers')[0]
          for layer_string in layers_string.split():
              _prefix, layer = layer_string.split('.')  # '//@layers.0' -> '0'
              layers.append(int(layer))
      return layers
docs: returns the layer ids from a SaltElement (i.e. a node, edge or layer).
  
      Parameters
      ----------
      element : lxml.etree._Element
          an etree element parsed from a SaltXML document
  
      Returns
      -------
      layers: list of int
          list of layer indices. list might be empty.