SGML (ISO 8879) has basically all these things: it infers tags (such as for opening paragraphs as in your example, but also infers missing html, head, and body

SGML (ISO 8879) has basically all these things: it infers tags (such as for opening paragraphs as in your example, but also infers missing html, head, and body tags, and also infers end-element tags for paragraphs, etc etc), has a built-in mechanism for recognizing custom tokens and turn those into tags to implement markdown and custom syntaxes, provides text macros, and many, many more things (including stylesheets, transformations for things such as table of content generation and search result views). In other words, SGML is complementing the HTML vocabulary with authoring affordances, as originally intended (HTML is based on it).