They want to be able to write logic to operate on the DOM elements rather than on Jinja2/Twig/etc template tags.

Twig has what it calls 'Live Components', which extend its HTML templating engine to update elements live over automatically linked AJAX calls. Basically turning its static templates into more of a react type system.

I think this sounds more like what the author means.

https://symfony.com/bundles/ux-live-component/current/index....