static void web_printMapping(Map<WebNode> mapping) {
  if (empty(mapping)) { print("-"); ret; }
  final Map<WebNode> rev = reversedMap(mapping);
  Web web = first(mapping.values()).web;
  L<Pair<WebNode>> relations = web_nonEmptyRelations(web);
   print("Web " + web.globalID + " from " + web.source + ": " + n(web.nodes, "node") + ", " + n(relations, "relation"));
  pnlIndent(map(web_nonRelationNodes(web), func(WebNode n) {
    WebNode src = rev.get(n);
    ret (src != null ? src.text() + " > " : "") + n.text();
  }));
  print();
  web_printRelations(web);
}