Currently we special case only a raw id selector. Patch forthcoming shortly to expand this to any selector with an id selector as its rightmost element, at a small cost in special case speed.
Changes results from:
div #title: 55ms
#title: 1ms (test variance? it shouldn't have sped up...)
div #title: 5ms
Created attachment 23745 [details]
Patch; Passes run-webkit-tests and doesn't regress http://ejohn.org/apps/selectortest/#target
Fixed in r36907