static MultiMap<S, WebNode> dw_fullNodeIndex_lower() {
  MultiMap<S, WebNode> index = treeMultiMap();
  for (Web web : downloadedWebs())
    for (WebNode node : web_nodes(web))
      for (S text : asSet(allToLower(node.texts())))
        index.put(text, node);
  ret index;
}