code: @Override
      public List<Offline> buildConstraint(BtrPlaceTree t, List<BtrpOperand> args) {
          if (checkConformance(t, args)) {
              @SuppressWarnings("unchecked")
              List<Node> ns = (List<Node>) params[0].transform(this, t, args.get(0));
              return ns != null ? Offline.newOffline(ns) : Collections.emptyList();
          }
          return Collections.emptyList();
      }
docs: Build an online constraint.
  
  @param args must be 1 scriptset of node. The set must not be empty
  @return a constraint