$unsafeValidationCallback_noArgs = [
	'type' => 'text',
	'validation-callback' => static function() {
		return $_GET['a'];
	}
];

$unsafeValidationCallback_oneArg = [
	'type' => 'text',
	'validation-callback' => static function ( $value ) {
		echo $value;
		return $value;
	}
];

$unsafeValidationCallback_twoArgs = [
	'type' => 'text',
	'validation-callback' => static function ( $value, $allData ) {
		echo $allData['foo'];
		return $allData['bar'];
	}
];

$safeValidationCallback = [
	'type' => 'text',
	'validation-callback' => static function ( $value, $allData ) {
		return htmlspecialchars( $value ) . htmlspecialchars( $allData['x'] );
	}
];

$unsafeCallback = static function ( $value ) {
	echo $value;
	return $value;
};

$indirectUnsafeValidationCallback = [
	'type' => 'text',
	'validation-callback' => $unsafeCallback,
];