Map<Element, Element> map = Maps.newTreeMap();
        for (Element element : keys) {
          map.put(element, element);
        }
        return map;
      }
    },
    SkipList {
      @Override
      Map<Element, Element> create(Collection<Element> keys) {
        Map<Element, Element> map = new ConcurrentSkipListMap<>();
        for (Element element : keys) {
          map.put(element, element);

*----+------+------+
| <<<*>>> | user properties, set from CLI with <<<-Dproperty=value>>> | <<<$\{skipTests\}>>> |
*----+------+------+
| <<<*>>> | model properties, such as project properties set in the pom | <<<$\{any.key\}>>> |
*----+------+------+