There are at least six competing formats for citations and cross-references in Markdown documents[0]. At some point, I'd like to update my text editor[1] to use a "standard" syntax, but CommonMark hasn't proposed one and the forums are quite quiet on the subject.

[0]: https://talk.commonmark.org/t/cross-references-and-citations...

[1]: https://github.com/DaveJarvis/keenwrite