It specifically makes the false claim that ISO C requires it to not be rejected, right there in what you quoted. ISO C requires no such thing. ISO C requires co

It specifically makes the false claim that ISO C requires it to not be rejected, right there in what you quoted. ISO C requires no such thing. ISO C requires compilers to diagnose it and allows them to choose whether to accept or to reject it. If compilers want to make it a hard error, they're perfectly free to do so. The fact that they don't is their choice, not something ISO C imposes on them.