You probably know that the Acid 3 score for nightly builds of WebKit was 90/100 last week. Today it’s up to 91/100 because I fixed our handling of DOM ranges under document mutation.
In older versions of WebKit, if you removed the node at one end of a DOM range from the document, the range would end up with one endpoint in the document and another endpoint outside the document. Ranges aren’t supposed to work that way. Instead, when you modify the document the range is supposed to get “fixed up” so that both endpoints are still in the document.
That’s fixed now and so Acid 3 test 13 now passes. See bug 11997 if you want to know more of the details.