The expanding use of key-val syntax in class and package options
means that packages can break due to unknown values.
I just tumble over this example in a real document:
I'm wondering what could/should be done to avoid such situations.
Should package authors avoid package options altogether and use
setup commands? Or can they (how?) parse the keys in the option list
in a way which doesn't gives errors but imply ignores unknown
values? Should the documentclass filter the options? How?