Is using :not(:not(+~>)) more efficient than using :has(+~>)?

[u-RraaLL]

Been wondering about it occasionally. Shouldn't using double :not() for siblings and children be more efficient than using a procedural filter? At least until :has() bacomes a native selector in the browsers as well?

[gothic-bum]

https://developer.mozilla.org/en-US/docs/Web/CSS/:not#description

The :not pseudo-class may not be nested, which means that :not(:not(...)) is invalid.

https://github.com/gorhill/uBlock/wiki/Procedural-cosmetic-filters#subjectnotarg

Note that if arg is valid CSS selector, uBO will not consider the :not operator to be a procedural one, it will rather consider the operator as being part of a CSS selector.

[gothic-bum]

@u-RraaLL

Update:

The use of :not(:not(...)) is specifically mentioned as being invalid with W3C Selectors Level 3:

Negations may not be nested; :not(:not(...)) is invalid.

However, it isn't mentioned with W3C Selectors Level 4, and per mdn/content#17313:

The current Level 4 spec removes any mention of this limitation.

But the MDN page for :not() still says:

The :not() pseudo-class requires a comma-separated list of one or more selectors as its argument. The list must not contain another negation selector or a pseudo-element.

[u-RraaLL]

Thanks, but this doesn't really matter. The :not(:not(...)) idea will be moot once we have :has(...) as a css selector.

... Maybe it could act as a non-forgiving version of :is(...), but I'm not sure.