[css-text] Syntax for percentage-of-width-of-space for 'word-spacing'

[fantasai]

We just resolved in #2165 to make percentages be relative to the current font size (like ems, but not computing to an absolute length for inheritance). That means we need a different syntax to represent a length proportional to the width of a space (that inherits as a proportion).

[faceless2]

An "sp" unit? This always struck me as an obvious gap in the font-related units, and it's no different to calculating "ch" or "ic"

[frivoal]

An "sp" unit? This always struck me as an obvious gap in the font-related units, and it's no different to calculating "ch" or "ic"

That would inherit as a length, and we're looking for something that inherits as a proportion.

An sp unit isn't inherently wrong, but it is sufficiently close to the ch unit that the demand isn't terribly strong.

[litherum]

A new unit is probably overkill for this. Perhaps just a function would work better?

[fantasai]

Alternately, just <number> could work. I know Tab hates it, but we're doing the same thing in tab-size also, so it'd be nice to be consistent.

[litherum]

I can't think of a good name for a function, so I think I slightly prefer a raw number.

[tabatkins]

I'm really against infecting more properties with "<number> as <length>"; it is impossible to calc() with for completely unnecessary technical reasons that authors shouldn't be exposed to.

[litherum]

If there was a function, could you calc inside it?

[tabatkins]

A function that resolved to a <length> could indeed be used in calc().

[litherum]

It looks like <length>s require units, but this new value represents a ratio or percentage.

How would one represent the concept of "Please set my word spacing to 130% of the space width" in a way that is compatible with calc()?

Would word-spacing: scale-space(calc(100% + 30%)) work?

Or maybe you're suggesting something like word-spacing: calc(scale-space(100% + 30%));?

[tabatkins]

The calc() problem I'm talking about is that, in a calculation, plain numbers need to be scalars: if a property takes a length, it's always valid to multiply the length by a scalar (5px * 3), and never valid to add it to a scalar (5px + 3). But if a number is a non-scalar value (a length), then this becomes impossible to adjudicate. If you start with a word-spacing: 1.3 and decide you need it to be 1px wider, you can't write word-spacing: calc(1.3 + 1px), because that fails to type-check, and there's no reasonable way around that. You need something to indicate that the non-scalar value is a non-scalar - a unit, a percentage sign, a function that we know evaluates to a non-scalar type like <length>, etc.

So yeah, if you wanted to use that last option, then word-spacing: calc(1px + scale-space(130%)) would work, it's just bit verbose.

(I personally think it's completely fine to have more single-use-case units, even or especially ones with longer names to indicate their special-purpose-ness. word-spacing: calc(1px + 1.3spacewidth) seems fine to me, and satisfies my objection from above.)