What matters for most (all?) tools is that the file is a valid HTML syntax. Most (all?) tools don’t care if the document it self is valid HTML. I don’t think I’ve used a single developer tool which stops working if I remove the <title> tag, nest <a> elements or even insert a self closing <div /> tag.

Vue uses @:[]. in their attributes and these are valid HTML attribute syntax. HTML attribute syntax only disallows SPACE"'>/= and some specific code points. Everything else is valid syntax.

https://vuejs.org/guide/essentials/template-syntax.html

https://html.spec.whatwg.org/#attributes-2

This is not the point, the point is if they are valid JavaScript or TypeScript.