protected function validateForbidden($input, $key)
    {
        $flat = NestedArray::flat($input);
        return !array_key_exists($key, $flat);
    }
protected function validateForbidden($input, $key)
    {
        $flat = NestedArray::flat($input);
        return !array_key_exists($key, $flat);
    }
protected function validateForbidden ( $ input , $ key ) { $ flat = NestedArray :: flat ( $ input ) ; return ! array_key_exists ( $ key , $ flat ) ; }
A validation rule. It fails if the key was found in the input.

@param array $input
@param string $key

@return bool
A validation rule . It fails if the key was found in the input .