[tannhaeuser]

FYI: the last time W3C, Inc. endorsed a WHATWG HTML snapshot as a recommendation was in 2021 ([1]), for the WHATWG snapshot published January, 2020 whereas the 2021 and 2022 snapshots were rejected, with no new review process having started since.

Reasons for rejection include a reporting API seen as privacy-invading and related disagreement over whether W3C's HTML WG could augment/redact WHATWG spec text like they used to be doing until 2017 when the previous HTML recommendation was published, or has to go through WHATWG process for any change according to the W3C/WHATWG "memorandum of understanding" which thus hasn't resulted in common understanding after all ;) Another reason was objection against the so-called HTML5 outlining algorithm, which Steve Faulkner actually has gone to great lenghts removing in WHATWG HTML upstream (cf. [2] for details).

Unfortunately, the removal also brought incompatible change to HTML (the content model of hgroup, among other incompatibilities), rendering existing content invalid, which WHATWG set out not to be doing but which they lack the methodology of preventing and for which the spec derived from Ian Hickson's work frankly lacks formal qualities to support. Even more unfortunate is that this change has already spilled to derived standards such as EPUB3 which hence makes existing EPUB3 content using compound headings going back to 2011 invalid, and EPUB3 writers lacking a tool for actually verifying what readers can support (epubcheck was blindly updated without consideration for the installed base). Technically, Review Draft January 2022 and newer should then already be called HTML 6. Since nobody gives a rat's ass (including W3C, Inc.'s dormant HTML WG) anyway, and gross misconceptions about HTML specs prevail, like in your post, I'm not sure whether we should call it a day with WHATWG/W3C's HTML specs already.

[1]: https://www.w3.org/blog/2021/whatwg-review-drafts-of-html-an...

[2]: https://sgmljs.net/blog/blog2303.html