"it'd be cool to produce error messages that lined up with MUST and MAY clauses." #readingToday
The States Language spec, of which I'm an author, should not surprise anyone; it's written somewhat in the style of an IETF RFC, full of MUST and MUST NOT and MAY as specified in RFC 2119.
When I sat down to write Statelint, it occurred to me that it'd be cool to produce error messages that lined up nicely with those MUST and MAY clauses. So I extracted them all into a file called StateMachine.j2119, where the "j" in the extension is for JSON.