It is now part of the spec: https://drafts.csswg.org/css-fonts-4/#valdef-font-size-absolute-size
<rdar://problem/101207950>
Pull request: https://github.com/WebKit/WebKit/pull/5418
Committed 255602@main (07860fac0bbf): <https://commits.webkit.org/255602@main> Reviewed commits have been landed. Closing PR #5418 and removing active labels.
Re-opening for pull request https://github.com/WebKit/WebKit/pull/5442
Committed 255629@main (3acc775bcb06): <https://commits.webkit.org/255629@main> Reviewed commits have been landed. Closing PR #5442 and removing active labels.