Metadata syntax (was Universal syntax for Markdown)

[David Sanson]

The reStructuredText field list syntax might be a reasonable compromise.

I like the fact that the metadata can occur anywhere in the document.

The [RST spec][] itself says that the leading colon can be dropped "in
well-defined contexts such as when a field list invariably occurs at
the beginning of a document (PEPs and email messages)." As John's
example from Hamlet shows, this isn't the case for markdown documents.
But it would be possible to grandfather in existing MMD documents by
insisting, as MMD does, that first lines that contain a colon are
unambiguously metadata, with apologies to Hamlet. Or one could
introduce a delimiter, like `--`, and say that lines before that
delimiter are unambiguously metadata, and so don't require the leading
colon.

Frankly, I don't think it wouldn't be a terrible thing if
implementations disagreed on this one detail---when is a leading colon
required?---but agreed on everything else. Those who wish to trade
flexibility for beauty could leave off the leading colon; those who
value inter-operability over beauty could leave it on.

David

[RST spec]: http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.html#field-lists