[tannhaeuser]

> messy HTML5 over "XHTML"

Nothing messy about HTML, whatever version. It just uses SGML features from a more civilized age, such as inferring tags not explicitly present when unambiguously required by the content model grammar.

Btw a large fragment of markdown can be implemented using SGML's SHORTREF feature, as can customizations such as GitHub-flavored markdown. John Gruber's markdown language is specified as a canonical rewriting into HTML with the option of inline HTML as fallback, making SGML SHORTREF a particularly fitting implementation model since it works just the same. It's quite striking how a technique for custom syntax invented in the 70's (however imperfectly specified, though not in a worse-is-better way lol) could foresee Wiki syntaxes and also determine the most commonly used markup language (HTML) fifty years later.

Agree with the gist of your post, though. As fantastic as MacFarlane's pandoc is, the idea to re-assign redundancies in markdown (eg. interpret minute presence/omission of space chars to mean something) was bound to fail, and that was very clear to me skimming only through a few paragraphs of the CommonMark manifesto. When it was first discussed here back then, someone commented that this was bound to happen when a logician (McFarlane) approached Wiki syntax.

[still_grokking]

SGML is a hot mess. It should have died decades ago.