code: private Set<Node> checkNegationSpecifier(NegationSpecifier specifier) throws NodeSelectorException {
          List<Selector> parts = new ArrayList<Selector>(1);
          parts.add(specifier.getSelector());
          return check(parts);
      }
docs: Check the {@link NegationSpecifier}.
  <p/>
  This method will add the {@link Selector} from the specifier in
  a list and invoke {@link #check(List)} with that list as the argument.
  
  @param specifier The negation specifier.
  @return A set of nodes after invoking {@link #check(List)}.
  @throws NodeSelectorException In case of an error.