Relevant spec sections:

https://drafts.csswg.org/selectors-4/#the-dir-pseudo
https://html.spec.whatwg.org/multipage/semantics-other.html#selector-ltr

The interesting cases to test are from the definition of "directionality" in HTML:
https://html.spec.whatwg.org/multipage/dom.html#the-directionality

• element with dir="ltr" matches :dir(ltr) (#26159)
• root element without `

While investigating the checkbox we found some sites had a toggle or switch state for their checkbox. This is not necessarily surprising as it can be seen here as well in the [switch](research concepts page).

I think to fully answer this question however there will need to be a bit more research as I'm truly asking from a graduation p

We should look at reducing the duplication between W3C and DINI profiles. If we have things that are share, those should move to "core/". We should otherwise export things from core/*.js that can be used by DINI.

See w3c/respec#2739 for specifics.

A DocumentFragment object exposes its innerHTML property, just like other Element objects do. This isn't a feature of the native DOMDocument, so it has to be exposed to IDEs using PHPDoc. Currently, accessing the innerHTML property works fine, but IDEs do not recognise the property.