374. Wrapped lines share a cross axis

Date: 2026-09-17

Status

Accepted. Closes book/src/TODO.md’s “align-content is still absent”.

Context

Align has nine constants and three of them — SPACE_BETWEEN, SPACE_AROUND and SPACE_EVENLY — are align-content only. align-content was not resolved, so those three were values the toolkit’s own enum advertised and no stylesheet could reach; worse, align-items: space-between parsed, because the keyword parser reads the whole enum, and then meant whatever Yoga does with a value CSS does not allow there.

The entry’s own argument for waiting was that nothing in the catalog wraps inside a box with a fixed height. That is still true, and it is an argument about a default rather than about a property: a wrapping container has a rule for its lines whether or not anybody wrote one.

Decision

align-content is resolved over the same [Align] value space, defaulting to stretch.

• stretch is Yoga’s default under useWebDefaults and CSS’s normal for a flex container, so every box in the catalog lays out exactly as it did.
• It reaches Yoga through YGNodeStyleSetAlignContent, which was bound on the first day and had no caller.
• Box.alignContent(Align) is the builder, beside alignItems and alignSelf.

Consequences

• The three constants that no property accepted are reachable, and reachable only from the property that means them.
• align-items: space-between is still admitted by the keyword parser and is still Yoga’s business what to do with — refusing per-property keyword subsets is a table this does not build.
• A wrapped row inside a fixed-height box can now pack its lines, which is what a future chip row inside a sized panel will want.