Motion and media capabilities

An authored capability record for motion and media enhancement gates and exact fallbacks.

Semantic page baseline

The shared foundations, Carousel, Marquee and Stagger are implemented. Try the media browser and motion preferences. Scroll Indicator and Cover Flow are also implemented. Image Gallery and its complete lightbox composition are implemented. Recorded capability probes remain separate from the real component interaction tests.

Reviewed 2026-08-26. These are locked browser probes, not detection of your browser or proof that a complete component is implemented.

Capability policy and declaration support

Native capabilities, optional presentation and deferred controls
Feature and source	Policy	chromium 151.0.7922.34	firefox 153.0	webkit 26.5	Fallback
anchorScope	optional	Detected	Detected	Detected	Snap native Dialog
animationRange	optional	Detected	Not detected	Detected	Static presentation
dialogCommands	required	Detected	Detected	Detected	Separate ordinary image destination
discreteTransitions	optional	Detected	Detected	Detected	Snap native Dialog
generatedControls	deferred	Detected	Not detected	Not detected	Real item links and native scroll
has	optional	Detected	Detected	Detected	Static list; preview unavailable
nativeScroll	required	Detected	Detected	Detected	Complete list and ordinary links
scrollSnap	optional	Detected	Detected	Detected	Native scrolling
scrollTimeline	optional	Detected	Not detected	Detected	Neutral track; no animation
timelineScope	optional	Detected	Not detected	Detected	Instance-local static presentation
transform3d	optional	Detected	Detected	Detected	Flat presentation
viewTimeline	optional	Detected	Not detected	Detected	Flat presentation

Observed behavior — separate from parsing

chromium 151.0.7922.34

checkboxGate: true
coverFlowTransform: true
dialogDismissed: true
dialogOpened: true
generatedControls: deferred
nativeScroll: true
originTransition: deferred-phase-5
scrollTimelineChanges: true
stationaryTimelineStable: true
viewTimelineChanges: true

firefox 153.0

checkboxGate: true
coverFlowTransform: false
dialogDismissed: true
dialogOpened: true
generatedControls: deferred
nativeScroll: true
originTransition: deferred-phase-5
scrollTimelineChanges: false
stationaryTimelineStable: true
viewTimelineChanges: false

webkit 26.5

checkboxGate: true
coverFlowTransform: true
dialogDismissed: true
dialogOpened: true
generatedControls: deferred
nativeScroll: true
originTransition: deferred-phase-5
scrollTimelineChanges: true
stationaryTimelineStable: true
viewTimelineChanges: true

Generated scroll controls and the optional gallery origin effect remain deferred. Unsupported timelines retain static native content; no script supplies a substitute.

Phase 4 actual component behavior

Actual generated HEEx and compiled CSS, not declaration parsing or visitor detection. Enhanced cases require wide containers, system motion permitted and no forced colors. All engines retain native content. Reviewed 2026-08-26.

chromium 151.0.7922.34: Scroll Indicator enhanced; Cover Flow enhanced.
firefox 153.0: Scroll Indicator neutral; Cover Flow flat.
webkit 26.5: Scroll Indicator enhanced; Cover Flow enhanced.

Run npm run browser:milestone-e-phase4 to verify native keys, isolated idle timelines, suppression and flat fallbacks. Narrow containers stay flat; no effect reports reading completion or a selected image.

Phase 5 native gallery and deferred origin effect

Chromium starts at the scoped thumbnail; Firefox and WebKit expose anchor/discrete declarations but no origin transition in this actual-modal probe. Defer the optional effect across this release; all engines use existing native snap Dialog.

chromium 151.0.7922.34: actual modal true; thumbnail-origin match true. Release presentation: native snap.
firefox 153.0: actual modal true; thumbnail-origin match false. Release presentation: native snap.
webkit 26.5: actual modal true; thumbnail-origin match false. Release presentation: native snap.

Reproduce with node scripts/record-gallery-origin.mjs --check and npm run browser:milestone-e-phase5. Test-only probe code and observations are excluded from the package.

Local media fixtures

Original geometric illustrations test aspect ratios, intrinsic sizing, captions and local publication. They are demo assets, not package dependencies.

Angular mountain ridges beneath a warm sun — 640 × 480. 413 bytes. MIT.

A white sailboat crossing a blue harbor — 720 × 480. 457 bytes. MIT.

Three evergreen trees on a low green hill — 480 × 640. 420 bytes. MIT.

Inspect intentional image failure

Intentionally unavailable landscape — This image is intentionally missing. Its caption and alternative text remain; open an available landscape.

Motion and replacement

Choose the component by its native behavior

Carousel is a complete scrollable list with real item links, not tabs or an automatically advancing slideshow.
Cover Flow decorates images in that same list; depth never means selection.
Scroll Indicator is decorative position in its own region. Use Progress for task completion or Meter for a scalar measurement.
Marquee is a static list with an optional finite preview. Stagger is a bounded entrance, not a visibility or application animation controller.
Image Gallery composes native Dialog. Its ordinary image destinations remain available without a lightbox or origin transition.

What remains when an enhancement is absent

Without scroll snap, use ordinary scrolling and item links. Without timelines, Cover Flow stays flat and Scroll Indicator stays neutral. Without anchor or transition support, the native dialog snaps open and closed. Generated scroll controls and origin transitions are deliberately deferred, even where declarations parse.

Failed images retain captions, alternative text and destinations. Lazy loading and async decoding are browser hints, not fetch-on-open, privacy or authorization guarantees. Applications own media rights and CSP. Finite previews may finish offscreen (Marquee at most five seconds, Stagger at most one); no observer pauses them.

Use System motion or Reduce motion in the header. System always respects your device setting. No force-animation choice exists. This evidence page itself starts no animation.

Native checkbox, scroll and dialog state can reset when the application replaces markup. Applications own patch boundaries and restoration; ShadcnUI adds no state manager.

Reproduce this evidence

npm run capabilities:motion-media:check
npm run browser:milestone-e-phase1

Run exact locked browsers and inspect fallbacks before claiming support. Source review and automatic checks do not replace keyboard and assistive-technology review.

Support and exact fallback

Motion and media capabilities support and fallback
Feature	Locked-engine evidence	When missing
Semantic page baseline	Controller and static-export tests exercise the same closed route.	Without optional gallery presentation, complete content and ordinary destinations remain in document order.

Without optional gallery presentation, complete content and ordinary destinations remain in document order.