code: def getChain(self) :
          "returns a list of keys representing the chain of documents"
          l = []
          h = self.head
          while h :
              l.append(h._key)
              h = h.nextDoc
          return f getChain(self) :
          "returns a list of keys representing the chain of documents"
          l = []
          h = self.head
          while h :
              l.append(h._key)
              h = h.nextDoc
          return l
docs: returns a list of keys representing the chain of documents