> is implementation-defined behavior, not undefined behavior. They're (confusingly) misusing the word "define" there. Implementation-defined behaviour is requi

> is implementation-defined behavior, not undefined behavior. They're (confusingly) misusing the word "define" there. Implementation-defined behaviour is required to be documented, but every behaviour is something that "you must define" in the sense that you have written down some (possibly implicit/emergent) definition of it as part of the compiler's source code. Ie, it's not "the standard requires you to define this", it's "you are not capable of not defining this, and the standard requires(C89)/doesn't require(C99+) you to pick from the following options".