[css-values-5] Add `number()` to coerce string values to numbers

[dead-claudia]

There's ident() for identifiers, and #12072 got me thinking it'd pair exceptionally well with counter(), like number(counter(name)).

Concretely, this could also be useful for ordering in some advanced use cases as well.

[dead-claudia]

Note: while alternative bases may be worth exploring, I'm specifically not proposing that at this stage.

Browsers can optimize number(counter(...)), by the way. It's as simple as just not stringifying the counter.

[tabatkins]

Are there use-cases for this other than counters? If not, avoiding the second call and just introducing counter-value(), as has been suggested in the past, is probably the right way to go.

(attr() already lets you parse directly into a number, so that's not a use.)

[dead-claudia]

Are there use-cases for this other than counters? If not, avoiding the second call and just introducing counter-value(), as has been suggested in the past, is probably the right way to go.

(attr() already lets you parse directly into a number, so that's not a use.)

There's no way to grab the content of an element as a number, either: https://drafts.csswg.org/css-content/#content-function. There may be others I'm also missing, as I haven't pored over all the specs in full.

If all of those gained ways to retrieve the same values as numbers with units, then that can replace this proposal.