}
protected void pushActiveScope( IdentityConstraint c, SelectorMatcher matcher ) {
LightStack s = (LightStack)activeScopes.get(c);
if(s==null)
activeScopes.put(c,s=new LightStack());
s.push(matcher);
}
protected void popActiveScope( IdentityConstraint c, SelectorMatcher matcher ) {
LightStack s = (LightStack)activeScopes.get(c);
if(s==null)
// since it's trying to pop, there must be a non-empty stack.