Function parse_class_check_list 

fn parse_class_check_list(
    list: &MetaList,
    check: ClassCheck,
) -> Result<ExplicitChecks>

inherits(...) / not_inherits(...) on a parameter (check says which): each string literal, and each class = "...", names one class (the argument must inherit from one of them, or from none of them); message = "..." gives the condition message of a failure, for all of them. No string is split on commas, as with inherits = "cls" (the method-level class = "a, b" is split, see parse_method_class_check).

inherits(...) also takes when(...) hints (#1824), each with its classes spelled the same way and a required message = "..." (parse_when_list).