It was useful in the initial development of WKContentRuleList, but is not useful any more.
Pull request: https://github.com/WebKit/WebKit/pull/3859
Committed 254019@main (5fd58c5a7062): <https://commits.webkit.org/254019@main> Reviewed commits have been landed. Closing PR #3859 and removing active labels.
<rdar://problem/99412449>