[DomCrawler] The doc about adding content in a crawler shows unsupported usages

[stof]

The doc at https://symfony.com/doc/current/components/dom_crawler.html#adding-the-content shows passing content inside the Crawler constructor and then calling add* methods on it. That's not a supported usage of the component.
You cannot mix multiple sources of content in the same Crawler instance. So a supported usage is to use either of the ways to add content, but not multiple ones like in this snippet.

See symfony/symfony#34950 for the original report.

[javiereguiluz]

Closing as fixed by #15212.