Since I'm not currently using GLM nor planning to for real-world code, I think it would be best if this is designed (and implemented) by actual users of GLM.
Some references: Getopt::Long::Descriptive (one_of, implies), Rinci::function (req_one, req_all, choose_one, choose_all, dep_any, dep_all, ...). Form libraries also typically have a way to specify this kind of thing.
Since I'm not currently using GLM nor planning to for real-world code, I think it would be best if this is designed (and implemented) by actual users of GLM.
Some references: Getopt::Long::Descriptive (one_of, implies), Rinci::function (req_one, req_all, choose_one, choose_all, dep_any, dep_all, ...). Form libraries also typically have a way to specify this kind of thing.