Patrick Steinhardt [off-list ref] writes:

Well, now that booleans are allowed I think we should just stop using
width specifiers like this altogether and instead use bool. There's
probably still going to be cases where we use those, but I assume that
the majority of users of this syntax is for flags.

Yeah, unless the structure with these members are designed to exist
in the millions in core (like "struct object" and its descendants),
bool is fine.