// *** before: ***
function createUser($name, $email, $isAdmin = false, $isActive = true) {
    // ...
}

createUser('Ann', 'ann@example.com', false, true);
// which positional argument is which? one has to check the signature

// *** in version 8.0: ***
createUser(
    name: 'Ann',
    email: 'ann@example.com',
    isActive: true,
    // isAdmin keeps its default, and order no longer matters
);