How to use the new :is() and :where() selectors with prefix

[zkmark]

I have the following code

:is( $prefix-class + btn:hover )} )

But when I compile it it gives me the following result

:is($prefix-class + btn:hover )} ) {
}

I would also like to know how to use those selectors within a class

:where()
https://developer.mozilla.org/en-US/docs/Web/CSS/:where

:es()
https://developer.mozilla.org/en-US/docs/Web/CSS/:is

It would also be nice if they added it to the documentation

By the way, in the documentation the Twitter link does not work, because the account is not active