Did you read the article? It said explicitly that regardless of `div.class a` or `div#id a` the same lookup takes place - every anchor on the page's parent is c

Did you read the article? It said explicitly that regardless of `div.class a` or `div#id a` the same lookup takes place - every anchor on the page's parent is checked to see if it has the id or class specified by the selector. So the selector `a#id` will be faster than `a.class` but a parent selector uses the same heuristic.