static HashMap<WebNode, WebNode> web_addNodesToWeb(Collection<WebNode> nodes, Web w) {
  new HashMap<WebNode, WebNode> map;
  if (empty(nodes)) ret map;
  Web web = first(nodes).web;
  for (WebNode node : nodes)
    map.put(node, cloneNodeToWeb(node, w));
  for (Pair<WebNode> p : keys(web.relations)) {
    WebNode a = map.get(p.a), b = map.get(p.b);
    if (a != null && b != null)
      w.getRelation(a, b).addLabels(web.getRelation(p).labels());
  }
  ret map;
}

Began life as a copy of #1009977