Petition from Sensei with the usecase being implementing strict options changing just between possible values and allowing custom ones for those that aren't.

Probably will be a default method with false for a while overridden by the default implementation.

Needs revising that the strict boolean always reflect that it's actually strict and doesn't change the way rules behave, given it has caused issue in the past (like #969), though IIRC some were fixed in the refactor given it not being exposed or used prevented a few.