[WorldMaker]

Needing multiple parts for a document is one of the older needs on the net (MIME's first RFC was 1992, for instance; though MIME would presumably be a terrible format for static site generators). Frontmatter seems related to HTTP headers, its just interesting to have needs for similar metadata for a file "at rest" as opposed to in transit.

Though HTTP does have an "at rest" relative, the META tag in HTML. Similarly, reStructuredText has always had "Field Lists" and even a history of using the first field list in a file as "frontmatter" and the docutils API even returns it as a separate metadata stream if asked. (Sphinx, for instance, checks for some fields there.) It's maybe just Markdown here that's deficient in having a first-class metadata syntax of its own. (reStructuredText and docutils also have a first-class concept of a document title made available by API to tools but maybe not intended for direct output in rendered contents, which is the number 1 reason for YAML front-matter in most Markdown documents I've seen.)