code: def update(self, other):
          
          if not isinstance(other, AttrTree):
              raise Exception('Can only update with another AttrTree type.')
          fixed_status = (self.fixed, other.fixed)
          (self.fixed, other.fixed) = (False, False)
          for identifier, element in other.items():
              if identifier not in self.data:
                  self[identifier] = element
              else:
                  self[identifier].update(element)
          (self.fixed, other.fixed) = fixed_status
docs: Updated the contents of the current AttrTree with the
          contents of a second AttrTree.