The idea is not so much on how to implement a feature, but more on adding markup syntax for an aliasing capability in Pandoc-flavoured Markdown.

Because SGML entities are just that, aliasing — DocBook authors know this well.

HTML entities, a targeted subset of SGML entities are an ageing solution — but ever so practical, for Unicode support.

HTML entities are finite. And can consequently be known and handled by Pandoc. As is the case today.

Markdown entities would be infinite. They adhere to the SGML reference syntax and are recognised as a new token type in the AST (or eventually as an HTML raw block).

Since they are recognised, you don’t need to intercept the AST and post process it before building your output.

A Pandoc writer cannot see HTML entities, they will have been converted to Unicode upstream.

Pandoc writers would see Markdown entities. They are cleanly marked in the AST and don’t need subsequent processing to be correctly parsed, they only need to be processed.

A writer no knowing how to process an entity should behave like an HTML browser with an unknown tag… ignore it.

HTML entities target Unicode. Markdown entities would simply be aliases for anything. I mentioned fonts, but that was a simplification.

As you see, using an existing markup syntax — such as DIVs, SPANs, or code blocks,  with attributes, is not what I target… though easy enough to code.

Merry Christmas to all