docs: def _ancestors(self):
          """Attribute referencing the tree ancestors of the node instance.
  
          :returns: list of node ancestors in sequence, first item is 
              the current node instance (`self`), the last item is root.
          :rtype: list of Node references
          """
          # return list of ancestor nodes starting with self.parent and ending with root
          _ancestors=[]
          _n = self
          while _n.parent:
              _n = _n.parent
              _ancestors.append(_n)
          return _ancestors