I have been studying AsciiDoc lately. It turns out to be a really hacked-together macro language for creating "ad-hoc lite markup" to "SGML/XML-based semantic markup" conversions. The core idea and the default ad-hoc lite markup are both pretty nice, but the implementation leaves a lot to be desired. AsciiDoctor is an alternative implementation which is used on GitHub and in other places, but I believe it interprets AsciiDoc as more of a "fixed format" like Markdown than the original reconfigurable macro-based approach.