This page says that if extending multiple interfaces with the same methods, the signature must be compatible. But this is not all there is to it: the order of `extends` matters. This is a known issue, and while it is disputable whether or not it is a bug, one should be aware of it, and code interfaces with this in mind.
https://bugs.php.net/bug.php?id=67270
https://bugs.php.net/bug.php?id=76361
https://bugs.php.net/bug.php?id=80785