code: public Collection<String> getChildElementNames() {
          if (childElementNames == null) {
              childElementNames = Collections.unmodifiableList(Arrays.asList(parseChildElementNameList()));
          }
          return childElementNames;
      }
docs: Gets a list of which elements the dependencies should be sorted after. Example:
  If the list returns "scope, groupId" then the dependencies should be sorted first by scope and then by
  groupId.
  
  @return a list of xml element names