The code to set selectorText parses the selector without the context of the stylesheet it's being parsed for. This makes parsing namespace prefixes fail.
<rdar://problem/102260326>
Pull request: https://github.com/WebKit/WebKit/pull/6414
Committed 256599@main (da821c38176a): <https://commits.webkit.org/256599@main> Reviewed commits have been landed. Closing PR #6414 and removing active labels.