feat: typography CSS keywords

[unpunnyfuns]

Changes

line-height: normal and letter-spacing: normal have no numeric form, both resolve from font metrics, so neither can be written as a ratio or a length.

Today there's no way to express them in DTCG.

Adds string to both slots in the typography sub-value type map, matching the carve-out paragraphSpacing and wordSpacing already have, and skips core/valid-number / core/valid-dimension for an allowlist: normal plus the five CSS-wide keywords.

Depends on #821, without it these keywords reach transformDimension and emit undefinedundefined. Shows two commits until that merges; the first is #821.

How to Review

• keywords.ts is the whole design. normal + initial | inherit | unset | revert | revert-layer (css-cascade-5 §defaulting-keywords). normal is the only property-specific keyword for either property.
• The rest is two guard calls and one line in the type map.

pnpm --filter @terrazzo/parser test: 2 new cases.

[changeset-bot]

🦋 Changeset detected

Latest commit: 4671c2b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 13 packages

Name	Type
@terrazzo/parser	Major
@terrazzo/token-tools	Major
@terrazzo/plugin-css-in-js	Major
@terrazzo/plugin-css	Major
@terrazzo/plugin-js	Major
@terrazzo/plugin-sass	Major
@terrazzo/plugin-swift	Major
@terrazzo/plugin-tailwind	Major
@terrazzo/plugin-token-listing	Major
@terrazzo/plugin-vanilla-extract	Major
@terrazzo/cli	Major
@terrazzo/token-types	Major
@terrazzo/use-color	Patch

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[unpunnyfuns]

Torn between matching CSS properly and keeping it a simple pass. More keywords exist than the two covered here. Would a strict/loose option help?

[Sidnioulz]

@drwpow for context, I brought up to @unpunnyfuns that in Swatchbook, we'd like to show normal when the CSS platform value is normal. This isn't quite the same as making it available directly at the parser level though. I think this PR could be a nice QoL deviation from the spec, but it could also be unwanted. I haven't taken the time to properly think about the implications of my ask, so there may need to be a discussion between us 3.

[unpunnyfuns]

I concur, this is more a QoL, and would stray from the narrow path.

[drwpow]

line-height: normal and letter-spacing: normal have no numeric form, both resolve from font metrics

My understanding is somewhat different, more aligning from MDN:

normal

Depends on the user agent. Desktop browsers (including Firefox) use a default value of roughly 1.2, depending on the element's font-family.

In my testing this is true—Firefox and Chrome seem to be 1.2, while Safari is ~1.1. The CSS spec seems to provide a rough calculation that user agents may not implement. And I’m not sure there’s an equivalent for native code.

---

The goal of DTCG is to encourage token values be universal and not CSS-first. But all that said, I’m not opposed to this addition so long as it’s opt-in for users. So I’d like to request 2 things:

1. core/valid-typography: add a allowCSSKeywords option, and document that this allows any CSS-valid keyword for lineHeight and letterSpacing. It should default to false
2. Remove the changes from valid-dimension.ts and valid-number.ts, and instead, add the bypass only in valid-typography.ts. This is more extensible and can prevent future bugs, by not introducing the idea that simple types are “aware” of their parent composite types

With both of these changes I’d be happy to accept this 🙂