return self::CONSTANT; // Fatal error
however that is actually allowed, what is an fatal error is
return Foo::CONSTANT; // Fatal error
compare
https://3v4l.org/dIeOk#v8.2rc7
https://3v4l.org/11of1#v8.2rc7
Prohibit direct access through a trait name
https://wiki.php.net/rfc/constants_in_traits