[att=val] selectors . And they work in all modern browsers in static form.
But when you will try to use such a selector with attributes changed from script you will get problems.
Following works as expected in FF but does not work in Google Chrome and Opera:
I am wondering why Opera and WebKit implementations are failed on this simple test.
As for my [educated] knowledge attribute value selector has the same complexity as e.g. class selector in CSS. No idea to be honest.