Per MDC, it "must be null (or not specified) for regular elements." As far as I can tell, this makes no difference in practice, because "null" and "undefined" are not pseudo element names, and don't even start with ":". But it seems cleaner not to pass them to DOM code.
Created attachment 73924 [details] proposed patch
Comment on attachment 73924 [details] proposed patch View in context: https://bugs.webkit.org/attachment.cgi?id=73924&action=review > WebCore/ChangeLog:8 > + No observable change in behavior, so no tests. Why do this if there is no observable change in behavior?
Comment on attachment 73924 [details] proposed patch Maybe we can change the default some day. I can’t remember how this relates to the similar properties in WebIDL.
Comment on attachment 73924 [details] proposed patch Well, basically it's just that I was surprised and confused to see "null" and "undefined" passed to DOM code when debugging.
Comment on attachment 73924 [details] proposed patch Clearing flags on attachment: 73924 Committed r72036: <http://trac.webkit.org/changeset/72036>
All reviewed patches have been landed. Closing bug.