Just a note/heads up for others that find themselves here...

I upgraded to v7.4.0-BETA1 - ran my unit tests, which worked in 7.3.x - and now they fail :)

Messages like:

Warning: DOMDocument::loadXML(): Failed to parse QName ':class' in Entity, line: 17 in /Users/phil/Sites/symfony-7.4-alpine-reproducer/vendor/symfony/dom-crawler/Crawler.php on line 1116

Warning: DOMDocument::loadXML(): error parsing attribute name in Entity, line: 21 in /Users/phil/Sites/symfony-7.4-alpine-reproducer/vendor/symfony/dom-crawler/Crawler.php on line 1116

A reproducer is here https://github.com/PhilETaylor/symfony-7.4-alpine-reproducer

I think this is a wont fix ...

Originally posted by @PhilETaylor in #61475 (comment)

Alpine JS is well known for not having valid HTML tags :( alpinejs/alpine#433

The Issue

PHP 8.4+ introduced a native HTML5 DOM parser. Symfony 7.4 automatically uses this native parser instead of the masterminds/html5 library.

However, the native parser is stricter about XML syntax and throws warnings when encountering Alpine.js shorthand attributes:

• @click → error parsing attribute name
• :class → Failed to parse QName ':class'
• @keydown.enter → error parsing attribute name
• Other Alpine.js shorthands → Various XML parsing errors

Why This Matters

In PHPUnit integration tests with failOnWarning="true":

1. Test uses KernelBrowser to request a page
2. Response contains HTML with Alpine.js attributes
3. Symfony's AbstractBrowser automatically creates Crawler from response
4. PHP 8.4's DOM parser emits warnings about Alpine.js attributes
5. PHPUnit converts warnings → test failures ❌