* to parse selectors (to complement the existing support for parsing rules,
    properties, values, etc.)
  * to return the list of applicable selectors for an element (rather than walk
    the public propertyHandlerMap property on AbstractCSSEngine)
  * add the ability to use "class" as an attribute, required to be able to query
    against the CSS class string (e.g., "CTabFolder[class='MPartStack']"
  * add associated tests
  * fix some possible NPEs