code: public static void exports(Xml root, CollisionConstraint constraint)
      {
          Check.notNull(root);
          Check.notNull(constraint);
  
          for (final Entry<Orientation, Collection<String>> entry : constraint.getConstraints().entrySet())
          {
              final Orientation orientation = entry.getKey();
  
              for (final String group : entry.getValue())
              {
                  final Xml current = root.createChild(NODE_CONSTRAINT);
                  current.writeString(ATT_ORIENTATION, orientation.name());
                  current.writeString(ATT_GROUP, group);
              }
          }
      }
docs: Export the collision constraint as a node.
  
  @param root The node root (must not be <code>null</code>).
  @param constraint The collision constraint to export (must not be <code>null</code>).
  @throws LionEngineException If error on writing.