See <COPYING.md> for details.
So I did this instead and it worked:
See [COPYING.md](COPYING.md) for details.
Should the first option have worked, according to the CommonMark spec? (i.e. should I report it as a bug to the maintainer)
If this isn’t in the spec, would it be a candidate for a suggestion? The first options is less verbose and more readable in regular unrendered text.