I didn't recognize the GSL citation, so for others:

- https://github.com/zeromq/gsl/blob/v4.1.5/examples/fsm_c.gsl

whew, this readme has everything

- XML in, text out: https://github.com/zeromq/gsl#:~:text=feed%20it%20some%20dat...

- a whole section on software engineering https://github.com/zeromq/gsl#model-oriented-programming

- they support COBOL https://github.com/zeromq/gsl#cobol

- and then a project 11 years old with "we're going to document these functions one day" https://github.com/zeromq/gsl#global-functions

What a journey that was