docs: def commentmap(self, cache=True):
          """return the comments from the docx, keyed to string id."""
          if self.__commentmap is not None and cache==True:
              return self.__commentmap
          else:
              x = self.xml(src='word/comments.xml')
              d = Dict()
              if x is None: return d
              for comment in x.root.xpath("w:comment", namespaces=self.NS):
                  id = comment.get("{%(w)s}id" % self.NS)
                  typ = comment.get("{%(w)s}type" % self.NS)
                  d[id] = Dict(id=id, type=typ, elem=comment)
              if cache==True: self.__commentmap = d
              return d