Coverage matrix

What each backend actually renders. A kind with no renderer draws a visible ⟨kind⟩ placeholder instead of failing, so these gaps are invisible in a screenshot — the showcase walkthrough asserts the same facts at runtime via assert_no_placeholders.

Built-in kinds

✓ = the backend’s realize handles it; · = it falls through to the placeholder.

kind	appkit	uikit	gtk	qt	xaml	android	arkui	dom
`day.container`	✓	✓	✓	✓	✓	✓	✓	✓
`day.label`	✓	✓	✓	✓	✓	✓	✓	✓
`day.button`	✓	✓	✓	✓	✓	✓	✓	✓
`day.toggle`	✓	✓	✓	✓	✓	✓	✓	✓
`day.slider`	✓	✓	✓	✓	✓	✓	✓	✓
`day.text_field`	✓	✓	✓	✓	✓	✓	✓	✓
`day.text_area`	✓	✓	✓	✓	✓	✓	✓	✓
`day.picker`	✓	✓	✓	✓	✓	✓	✓	✓
`day.divider`	✓	✓	✓	✓	✓	✓	✓	✓
`day.scroll`	✓	✓	✓	✓	✓	✓	✓	✓
`day.image`	✓	✓	✓	✓	✓	✓	✓	✓
`day.progress`	✓	✓	✓	✓	✓	✓	✓	✓
`day.canvas`	✓	✓	✓	✓	✓	✓	✓	✓
`day.nav`	✓	✓	✓	✓	✓	✓	✓	✓
`day.nav_page`	✓	✓	✓	✓	✓	✓	✓	✓
`day.nav_menu`	✓	✓	✓	✓	✓	✓	✓	✓
`day.list`	✓	✓	✓	✓	✓	✓	✓	✓
`day.tree`	✓	✓	✓	✓	✓	✓	·	·
`day.cover`	✓	✓	✓	✓	✓	✓	✓	✓
`day.inspector`	✓	·	✓	✓	✓	·	·	·
`day.inspector_pane`	✓	·	✓	✓	✓	·	·	·
`day.split`	✓	·	✓	✓	·	·	·	·
`day.split_pane`	✓	·	✓	✓	·	·	·	·
`day.list_item`	✓	✓	✓	·	·	✓	·	·

External pieces

✓ = the crate ships that backend’s renderer arm; · = no arm, so the kind renders the placeholder. A piece may still be absent at runtime if the app does not enable its feature.

A · is not always a gap: day-piece-colorpicker answers android and arkui with a picker COMPOSED from ordinary pieces, which by construction registers no renderer for its kind (colorpicker.md). This table measures arms, so it cannot see that — nothing derived from realize can.

piece	kind(s)	appkit	uikit	gtk	qt	xaml	android	arkui	dom
`day-piece-activity`	`day.piece.activity`	✓	✓	✓	✓	✓	✓	✓	·
`day-piece-colorpicker`	`day.piece.colorpicker`	✓	✓	✓	✓	✓	·	·	✓
`day-piece-combobox`	`day.piece.combobox`	✓	·	✓	✓	✓	✓	✓	·
`day-piece-datetime`	`day.piece.datepicker`, `day.piece.timepicker`	✓	✓	✓	✓	✓	✓	✓	✓
`day-piece-map`	`day.piece.map`	✓	✓	·	·	·	·	·	·
`day-piece-pager`	`day.piece.pager`	·	✓	·	·	·	✓	✓	·
`day-piece-pullrefresh`	`day.piece.pullrefresh`	·	✓	·	·	·	✓	✓	·
`day-piece-remote-image`	`day.piece.remote_image`	✓	✓	✓	✓	✓	✓	✓	·
`day-piece-searchfield`	`day.piece.searchfield`	✓	✓	✓	✓	✓	✓	✓	·
`day-piece-stepper`	`day.piece.stepper`	✓	·	✓	✓	·	·	·	·
`day-piece-swiftui`	`day.piece.swiftui`	✓	✓	·	·	·	·	·	·
`day-piece-texteditor`	`day.piece.texteditor`	✓	✓	✓	✓	✓	✓	✓	✓

Capabilities

What each backend answers for Cap (capability()): N native, E emulated, – unsupported, ? decided at runtime (day-dom answers NavSplit from the viewport width; day-qt answers WindowTabbing natively on macOS alone). An app branches on this rather than on the target name.

cap	appkit	uikit	gtk	qt	xaml	android	arkui	dom
`DragDrop`	N	N	N	N	N	N	N	N
`DragExternalImport`	N	N	N	N	N	N	N	N
`DragExternalExport`	N	N	N	N	N	N	N	–
`DragMultipleItems`	N	N	N	N	N	N	N	N
`DragFileReferences`	N	–	N	N	N	–	–	–
`DragDeferredReceipt`	–	–	N	–	N	–	–	–
`DragFilePromises`	–	–	–	–	–	–	–	–
`DragExternalMove`	–	–	–	–	–	–	–	–
`ListRecycling`	N	N	N	N	N	N	N	E
`UndoBridge`	N	N	–	–	–	–	–	–
`EditBridge`	N	N	–	–	–	–	–	N
`ListReorder`	N	N	N	N	N	N	N	E
`NavReorder`	N	–	N	N	N	–	N	E
`ListDelete`	–	N	–	–	N	N	N	–
`ListSwipeActions`	N	N	–	–	N	–	–	–
`ListEditing`	–	N	–	–	–	–	–	–
`ListItem`	N	N	N	–	–	N	–	–
`Tree`	N	N	N	N	N	E	E	E
`TreeMove`	N	–	–	–	–	–	–	–
`TreeSections`	N	N	N	N	N	N	E	E
`BaselineAlignment`	N	E	N	E	E	N	E	E
`TextRuns`	N	N	N	N	N	N	N	N
`TextLinks`	N	N	N	N	N	N	N	N
`Lottie`	–	–	–	–	–	–	–	–
`NativeSymbols`	N	–	–	–	–	–	–	–
`Snapshot`	N	N	N	N	N	N	N	–
`NavSplit`	N	N	N	N	N	N	N	N
`NavTabs`	N	N	N	N	N	N	E	E
`NavTabsAdaptive`	–	N	–	–	–	N	E	E
`NavRepresent`	N	E	–	N	–	E	E	N
`NavContentList`	N	E	N	N	–	–	–	–
`NavHeader`	–	N	–	–	N	N	N	–
`Appearance`	N	N	N	–	N	?	?	N
`AppMenu`	N	–	N	N	N	–	–	E
`Dialogs`	N	N	N	N	N	N	N	N
`FileDialogs`	N	N	N	N	N	N	N	N
`Animation`	N	N	N	N	N	N	N	N
`Cover`	E	N	E	E	E	N	E	E
`CoverSheet`	N	N	–	–	–	–	–	–
`StatusBarHidden`	–	N	–	–	–	N	N	–
`TextEditable`	N	N	N	N	N	N	E	N
`TextSelectable`	N	N	–	N	E	N	E	N
`TextSpellCheck`	N	N	–	–	N	N	–	N
`MultiWindow`	N	?	N	N	N	N	?	–
`AppBadgeCount`	N	N	?	?	N	–	?	E
`AppBadgeText`	N	–	–	–	–	–	–	–
`AppBadgeDot`	N	–	–	–	N	–	–	E
`Toolbar`	N	N	N	N	N	N	E	E
`ToolbarSearch`	N	–	N	N	N	–	–	E
`Inspector`	N	–	N	N	N	–	–	–
`Split`	N	–	N	N	–	–	–	–
`Cursor`	N	E	N	E	E	N	–	N
`FontList`	N	N	N	N	N	N	N	E
`ReduceMotion`	N	N	N	–	N	N	?	N
`Announce`	N	N	?	?	N	N	?	E
`ImageDecode`	N	N	N	N	N	N	N	N
`ImageEncode`	N	N	N	N	N	N	N	N
`ImageProperties`	N	–	–	–	–	–	–	–
`CanvasBitmap`	N	N	N	N	N	N	N	N
`CanvasPdf`	N	N	N	N	–	N	–	–
`WindowStates`	N	–	N	N	N	–	–	–
`WindowFullscreen`	N	E	N	N	N	N	?	?
`ContentProtection`	N	E	–	–	N	N	?	–
`WindowTabbing`	N	–	–	?	–	–	–	–
`DockMenu`	N	–	–	–	–	–	–	–
`WindowGeometry`	N	–	N	N	N	–	–	–
`WindowPosition`	N	–	–	?	N	–	–	–
`WindowLevel`	N	–	–	N	N	–	–	–
`WindowAppearance`	N	N	–	–	N	–	–	E
`RequestAttention`	N	–	–	N	N	–	–	–
`FramelessWindow`	N	–	N	N	N	–	–	–
`OverlayTitleBar`	N	–	N	–	N	–	–	?
`TransparentWindow`	N	–	?	N	–	–	–	–
`WindowMaterial`	N	–	–	–	?	–	–	–
`DragRegion`	N	–	N	N	N	–	–	?
`StatusItem`	N	–	?	?	N	–	–	–
`AppProgress`	N	–	?	?	N	–	–	–
`DockVisibility`	N	–	–	–	–	–	–	–
`Monitors`	N	E	N	N	N	E	E	E
`DynamicShortcuts`	N	N	–	–	N	?	–	–