Yii2 validation with XRegExp, p{L} not working

I’m using Yii2 framework and I have a Validator that should do client-side validation. I have a regex that looks like this: /^[\p{L}]+$/u for simplicity, but my actual regex is a bit more complicated, but the p{L} part is what causes the problems.

And so my code like this in the validator class:

public function clientValidateAttribute($model, $attribute, $view)
{
    $message = json_encode($this->message, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
    return <<<JS
    if (!XRegExp('/^[\p{L}]+$/u').test(value)) {
        messages.push($message);
    }
JS;
}

Problem is, this always fails for p{L} but if I change the pattern for something like /^[A-Z]+$/ it works flawlessly.

I’m using the 1.3.0 xregexp-all.js. It is added to in an AssetBundle class in assetsAppAsset.php

Answer

I did notice while I was playing around with my regex, that when I made it wrong and was shown an exception, \p{L} was interpreted as p{L}. So after some tries I’ve found out that for whatever reason I needed four backslashes to get it interpreted as p{L}. Final code that works:

public function clientValidateAttribute($model, $attribute, $view)
{
    $message = json_encode($this->message, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
    return <<<JS
    if(!XRegExp('^[\\p{L}]+$').test(value)) {
        messages.push($message);
    }
JS;
}