pseudo-class CHECKED and general sibling ~ combinator

Hi,
can you implemented pseudo-class checked? I think it could be like that:

```
private static class CheckedCondition extends Condition {
CheckedCondition() {
}
@Override
boolean matches(Object e, AttributeResolver attRes, TreeResolver treeRes) {
String result = attRes.getAttributeValue(e, "checked");
return result != null;
}
}
```

But I really dont know how implemented general sibling combinator (~ tilde)...