Upgrade to 4.2.0

kirby/src/Toolkit/V.php

@@ -283,6 +283,14 @@ V::$validators = [
 			V::max($value, $max) === true;
 	},
 
+	/**
+	 * Checks with the callback sent by the user
+	 * It's ideal for one-time custom validations
+	 */
+	'callback' => function ($value, callable $callback): bool {
+		return $callback($value);
+	},
+
 	/**
 	 * Checks if the given string contains the given value
 	 */