docs: def node_branch(self, al_keys, al_values):
              """
              For each node in <al_values>, add to internal contents
              dictionary using key from <al_keys>.
              """
              if len(al_keys) != len(al_values):
                  self.error_exit("adding branch nodes", "#keys != #values", 1)
              ldict = dict(zip(al_keys, al_values))
              self.node_dictBranch(ldict)