JS called from the head (without "async") blocks all further progress, but I don't think CSS necesarily does. (Though of course the page can't actually render to the screen without all the CSS.) SO seems to back that view up: http://stackoverflow.com/questions/4026183/as-javascript-in-... YMMV in older versions of IE. I think everything blocks with them.

I'm not sure about ready vs load, but that would make sense.