Number of columns. For CardArea layouts: 1-5 or 'auto' (dynamic based on screen width). For GroupedElementsArea: GroupElement-grid pattern (e.g. 'auto', '2', '2,1' for tablet-landscape/tablet-portrait/phone). When set on a GroupedElementsArea, child GroupElements without their own 'columns' attribute inherit this value. Layout strategy for Card areas in Lumina: 'grid' (CSS grid with equal heights and colSpan support) or 'floating' (reading-order float columns with dynamic heights). Default: 'grid' for schemaVersion >= 2, 'floating' for older contracts. Can be overridden per section by RowHeader layout. RowHeader component for collapsible card row sections in Lumina layouts. Controls visibility of all CardContainers that follow until the next RowHeader. Supported bindings: Title (Label), IsCollapsible (boolean), CollapseState (boolean, TWO_WAY) Overrides the Area's layout for all CardContainers following this RowHeader until the next RowHeader. Values: 'grid' (CSS grid with equal heights) or 'floating' (reading-order float columns with dynamic heights). Overrides the Area's columns for all CardContainers following this RowHeader. Values: 1-5 or 'auto'. Lumina header component for an Area: optional title on the left, optional action children on the right. Action children must be ImageButton (or ButtonGroup wrapping ImageButtons). Use Binding type="Visible" on children for runtime visibility; the static directlyVisible="false" attribute is honored at layout level only. Number of grid columns this card spans (1 to columns). Used with Area columns attribute in Lumina. Card height mode: 'fixed' (375px, default) or 'dynamic' (grows with content) Placeholder element that controls where the Quick Action Card is positioned within a CardArea. The card is populated at runtime with quick action data when the feature is enabled and actions are available. Only one QuickActionCardContainer is allowed per CardArea. Supports Bindings for Title, Visible, IsCollapsible, and CollapseState. Text display component for CardContainer. Text fills available space and is clipped at the container boundary. When true, shows a blue vertical indicator on the left of the selected row. Supported only for Lumina or higher (schemaVersion >= 2.0). Default: false. Optional rendering mode override. 'legacy' renders the contract without Lumina chrome, 'compatibility' applies Lumina chrome but preserves legacy metrics (sizes, paddings, em-base), 'lumina' applies the complete Lumina rendering including metrics. Honored only when activation is on. schemaVersion >= 2 contracts always render in 'lumina' mode; explicit 'legacy' or 'compatibility' on a schemaVersion >= 2 contract is rejected by code-based validation.