Static grid (box.type: grid)

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An explicit box.type: grid on a container (or repeat cell / repeat_flow card) tiles its children into column tracks instead of a flex stack. Grid is explicit-only: grid keys without type: grid warn grid_key_ignored rather than implying a mode switch.

Syntax

- type: container
  box: { type: grid, columns: ["30%", "70%"], rowGap: 4 }
  items:              # row-major: label, value, label, value, …
    - { type: text, text: "小計" }
    - { type: text, text: "{amount.subtotal}", style: { textAlign: right } }
    - { type: text, text: "合計" }
    - { type: text, text: "{amount.total}", style: { textAlign: right } }

Keys (on the container's box)

Key	Values	Default	Description
type	grid	—	Required to activate grid placement.
columns	count | list of Length/fr/auto	1 column	Column tracks: a count (equal split of the content width minus gaps) or a track list (["auto", "1fr", "30%", 50], any Length, fr weight — see fr weights — and/or auto, sized to the widest cell placed in the track).
rows	count | list of Length/fr/auto	auto rows	A count needs a definite container height (auto-height degrades to auto rows with a diagnostic); rows beyond an explicit list are implicit — auto, sized by their tallest child. Writing auto in the list says exactly that, so ["auto", "1fr"] reads the way it looks. An fr row needs a definite height (auto-height degrades with grid_fr_no_basis).
columnGap / rowGap	Length	0	Per-axis gaps; the flex gap doubles as the both-axes shorthand (specific keys win). Negative gaps are 0.
direction	row | column	row	Fill order (CSS grid-auto-flow analog): row = row-major.
justifyContent	flex values	start	Distributes leftover width across tracks (only meaningful for track lists — counts consume the axis).
alignItems	flex values	stretch	Aligns children within their row (with vertical auto margins).

Child keys (on a grid child's box, like flexGrow in flex):

Key	Values	Default	Description
columnSpan	count ≥ 1	1	How many column tracks the child spans; the cell run is the spanned widths plus the gaps between them. Clamped to the track count (grid_span_clamped).
rowSpan	count ≥ 1	1	How many row tracks the child spans; cells beneath are reserved. Clamped to 64 (grid_span_clamped).

Behavior

• Fill order is document order along direction. The participation rule is the flex one: authored box.x/box.y = absolute escape hatch.
• Spans consume a rectangle of cells from an occupancy map: each child takes the first free run that fits in fill order (a span that cannot fit in the row's remaining columns wraps whole). A row-spanning child pours any height its spanned rows don't cover into its last spanned auto row (the v1 distribution); over explicit tracks it warns grid_cell_overflow instead. Span keys outside a type: grid parent warn span_outside_grid and are inert.
• Cells: a child fills its track width (% resolves against the cell); horizontal auto margins center/push within the cell. A child taller than its explicit row track warns grid_cell_overflow and overflows visually, CSS-like — to clip, author overflow: hidden on the child container itself. A child wider than its column-track run warns grid_column_overflow (its own code, carrying only numbers — child/track/span — so a translating consumer writes its own sentence). A definite-width child either fits its track run or spills over its neighbour; a child with no authored w fills the run and never warns. Sizing a track to its content is what auto columns are for.
• Caps: track counts and list lengths clamp to MAX_GRID_TRACKS (64) per axis with grid_tracks_clamped, so hostile counts cannot drive allocation.

fr weights

A track in a list may be an fr weight ("1fr", "2.5fr") instead of a fixed Length. After the fixed tracks and the gaps are subtracted from the axis, the leftover distributes across the fr tracks in proportion to their weights — the same machinery as flex flexGrow:

box: { type: grid, columns: ["1fr", "2fr", 90] }   # 90pt fixed; the
                                                   # rest splits 1:2

• fr is a grid-track-only unit — it is not a Length, so "1fr" anywhere a plain length is expected (box w, margins, gaps, column widths) is an "invalid length" parse error.
• Weights must be finite and non-negative (parse-rejected otherwise); a 0fr track takes no leftover. When the fixed tracks already fill (or overflow) the axis, fr tracks collapse to 0. All-zero weights degrade to an equal split.
• Columns always have a width basis, so column fr always resolves. Rows need a definite container height (like a row count); an auto-height container degrades fr rows to auto with grid_fr_no_basis.
• An fr row splits the leftover after the fixed rows, the gaps and the auto rows — mixing fr rows with auto or implicit content rows in one definite-height grid works, and the auto rows are measured before the split rather than counting as nothing.
• Limitation: a row-SPANNING child does not feed that measurement. A span pours its overflow into its LAST spanned row only once the rows it covers have sizes, and one of those is the fr size being computed — genuinely circular, unlike the column case. So an auto row whose extra height would have come from a span is measured without it, and the fr rows take slightly more than they should. Keep row-spanning children out of grids that mix fr with auto rows, or give those rows fixed heights.

auto tracks

A track in a list may also be auto. An auto column is as wide as the widest cell placed in it — its content width, the width at which that cell's text would not wrap:

box: { type: grid, columns: ["auto", "1fr"] }   # label column fits its
                                                # text; the rest follows

• Sizing runs before the cells are laid out, which is why the grid assigns cells first and sizes tracks second. fr tracks still take whatever is left after the fixed and auto ones.
• Only children occupying a single column contribute a width. CSS spreads a spanning child's demand across the tracks it covers; doing that needs the other tracks' sizes, which is the circularity this ordering avoids. An auto column holding nothing but spanning children therefore sizes to 0.
• Content is measured with no container to bound it, so a long unwrapped string can ask for more than the whole grid. The auto tracks then scale down together to what is actually there, and the content wraps inside them.
• The measurement is the same one flex flexBasis: content uses, so the kinds with no max-content width are the same — see the list on flex.md. A cell with an authored w contributes that width directly.
• auto in a row list is the implicit auto row (as tall as its tallest child), which is what omitting the entry already means. It adds no machinery; it is accepted so a mixed list reads plainly.
• Like fr, auto is grid-track-only — "auto" where a plain length is expected is a parse error, and older engines reject it the same way.

Limitations

• Explicit only: grid keys without box.type: grid are ignored (grid_key_ignored) and never imply the mode.
• 1..=64 tracks per axis (grid_tracks_clamped); a columnSpan/rowSpan past the axis is clamped (grid_span_clamped).
• fr ROW tracks need a definite height. In an auto-height container they size as auto rows instead (grid_fr_no_basis).
• A child wider than its track run spills over its neighbour (grid_column_overflow); taller than an EXPLICIT row track it warns (grid_cell_overflow) — auto rows grow instead.
• Span keys on a child of a non-grid box are inert (span_outside_grid).
• No named areas and no auto-placement algorithm: children fill the tracks in order.

Diagnostics

Code	Meaning
grid_tracks_clamped	columns/rows outside 1..=64 tracks (or an empty list); clamped
grid_cell_overflow	child TALLER than its explicit row track; overflows visually
grid_column_overflow	child WIDER than the column-track run it spans; overflows visually
grid_key_ignored	grid keys authored without box.type: grid
grid_span_clamped	columnSpan/rowSpan beyond the axis; clamped
span_outside_grid	span keys on a child of a non-grid box; ignored
grid_fr_no_basis	fr row tracks in an auto-height container; sized as auto rows

Capability keys: box.grid, grid.span, grid.fr.

See also

• flex.md — the default mode and the shared alignment keys
• repeat.md — the data-driven grid (one cell per array element)