protected StyleGroup addElement_(Element element) {
ArrayList<Rule> rules = stylesheet.getRulesFor(element);
String gid = stylesheet.getStyleGroupIdFor(element, rules);
StyleGroup group = groups.get(gid);
if (group == null) group = addGroup(gid, rules, element);
else group.addElement(element);
addElementToReverseSearch(element, gid);
return group;
}
