code: func (o *orderedDict) keys() isolated.HexDigests {
  	out := make(isolated.HexDigests, 0, o.length())
  	for e := o.ll.Front(); e != nil; e = e.Next() {
  		out = append(out, e.Value.(*entry).key)
  	}
  	return out
  }
docs: // keys returns the keys in order.