code: public void addMatch(Element e, PseudoClassType pseudoClass)
      {
          if (elements == null)
              elements = new HashMap<Element, Set<PseudoClassType>>();
          
          Set<PseudoClassType> classes = elements.get(e);
          if (classes == null)
          {
              classes = new HashSet<PseudoClassType>(2);
              elements.put(e, classes);
          }
          classes.add(pseudoClass);
      }
docs: Assigns a pseudo class to the given element. Multiple pseudo classes may be assigned to a single element.
  @param e the DOM element
  @param pseudoClass the pseudo class to be assigned