This is a special constraint for ConfirmedPasswordField, so you can add separate constraints on the PasswordField and ConfirmPasswordField, and also will automatically make sure the ConfirmPasswordField has the same value as PasswordField.
$validator = ZenValidator::create();
$validator->setConstraint(
$field,
new \Milkyway\SS\ZenForms\Constraints\ConfirmPassword([
'PasswordField' => [
new Constraint_required(),
new \Milkyway\SS\ZenForms\Constraints\ValidPassword(Member::password_validator()),
],
'ConfirmedPasswordField' => [
new Constraint_required(),
],
])
);