code: def update(self, name):
          
  
          if name is None:
              return
  
          if name not in self._names:
              # add the name if it isn't already tracked
              self._names[name] = len(self._names)
  
          result = self._names[name] - self._current
          self._current = self._names[name]
          return result
docs: Query a name for the relative index value to be added into the
          source map name field (optional 5th element).