A number of static site generators and/or Markdown implementations
support the notion of a "front matter", a (normally) YAML list pre-
pended before the document text, containing document metadata. E.g.:

    ---
    title: how to blog
    author: Joe Bloggs
    ---
    document goes here

IkiWiki has (currently) made a deliberate decision not to support these (or
more precisely, the similar but different Pandoc-style block with lines
prefixed by '%'). Quoting `mdwn.pm` (here in the section that handles
*Discount*):

    # Disable Pandoc-style % Title, % Author, % Date
    # Use the meta plugin instead
    $always_flags |= Text::Markdown::Discount::MKD_NOHEADER();

It would be good to support YAML-formatted pre-pended metadata,
translating recognised keys into [[plugins/meta]] definitions, to aid
migration between IkiWiki and other static site generators: it
would aid the same source files being useable in multiple systems.

This would require the `mdwn` plugin to be more closely-coupled to
the `meta` plugin, but not the reverse. I think this wouldn't be a
big problem, as the prospect of an IkiWiki site that was using the
`mdwn` plugin but *not* the `meta` plugin is fairly remote. And we
could make front-matter handling configurably on or off.

References:
 * [Pandoc extension yaml_metadata_block](https://pandoc.org/MANUAL.html#extension-yaml_metadata_block)
 * [Hakyll 'pages and metadata'](https://jaspervdj.be/hakyll/tutorials/02-basics.html#pages-and-metadata)
 * [Jekyll 'front matter'](https://jekyllrb.com/docs/front-matter/)

*— [[Jon]], 2021-10-15*