Spawned from https://github.com/WebKit/WebKit/pull/10227#discussion_r1112342342 Because the "subtitle" attribute is only used in the non-standard Attachment element, it shouldn't be part of the list of standard HTML attribute names. <rdar://105697448>
Pull request: https://github.com/WebKit/WebKit/pull/10501
Committed 260696@main (87c8ca6824e5): <https://commits.webkit.org/260696@main> Reviewed commits have been landed. Closing PR #10501 and removing active labels.