hyperframes/skills/hyperframes-core/references/data-attributes.md

Data Attributes Reference

Every HyperFrames composition uses data-* attributes to declare timing and structure to the framework. This is the full attribute table — pair with tracks-and-clips.md for the rules behind data-track-index.

Composition Root

Every renderable composition needs one root element:

Attribute	Required	Meaning
data-composition-id	Yes	Unique ID. Must match the animation registry key on window.__timelines.
data-width / data-height	Yes	Pixel frame size. Common values: 1920x1080, 1080x1920, 1080x1080.
data-duration	Conditional*	Render duration in seconds (total length / frame count), not the GSAP timeline length. Read once at compile time, like data-width / data-height: a static root data-duration is locked before scripts run, so a script (root.setAttribute("data-duration", ...)) or a --variables-driven value cannot change the render length. To vary length per render, author the root data-duration directly. (A clip's data-duration is different: re-read from the live DOM, so scripts/variables can drive it.) Only when the root omits data-duration does the renderer derive total length from the live DOM / timeline after scripts run.
data-fps	No	Optional frame rate hint. CLI render flags can override output fps.
data-composition-variables	No	JSON array of variable declarations (on <html>). See variables-and-media.md.

*data-duration is optional whenever the runtime can auto-infer duration: a registered GSAP timeline, a finite CSS animation, a finite WAAPI element.animate(), a registered Lottie animation, or timed clips (the root then ends at its latest clip end, and lint only warns root_composition_duration_derived). It is required for Three.js (no auto-inference), for infinite/unbounded CSS or WAAPI animations, and for any composition with no GSAP timeline, no animation signal and no timed clip with a length. npx hyperframes lint enforces this (root_composition_missing_duration_source). Per-runtime inference lives in hyperframes-animation/adapters/.

The root should be position: relative, have explicit pixel dimensions, and hide overflow unless intentionally composing outside the frame.

Clip Attributes

data-start is what makes an element a clip. The runtime collects [data-start] and drives visibility off that attribute, so any element carrying it is timed.

class="clip" is a convention, not a requirement: the runtime never reads it. Keep writing it: drop it and the full-frame box collapses unless you supply that layout yourself, Studio uses it as an edit hint, and lint warns (timed_element_missing_clip_class) when a timed element lacks it. Omit it on <video> and <audio>.

Nesting is allowed. A timed element inside a wrapper is still timed, and a timed ancestor clamps its descendants: a child cannot be visible while its timed ancestor is hidden. Direct children of the root get automatic layout (see "Root-level clips get automatic layout" below); nested ones do not, so give them their own positioning.

Attribute	Required	Meaning
id	Yes on <video>/<audio>, else recommended	lint errors with media_missing_id on media without one, and an id-less <audio> is never mixed, so the render is silent. Elsewhere it is a warning (studio_missing_editable_id): Studio needs a stable edit target, and timeline targets reference it.
data-start	Yes	Start time in seconds, or a supported clip-time reference. This attribute is what marks the element as timed.
data-duration	Required for div and sub-compositions	Duration in seconds. An img with data-start defaults to 3 s; video/audio default to the source length (less the playback offset, over the rate) once known; an authored value trims. Without any resolvable duration the element has no end and stays visible for the rest of the composition.
data-track-index	No	Studio timeline lane, display only. The render never reads it, and clips on one track may overlap in time. Absent, the parser defaults it and Studio lays out one lane per clip. Two <audio> elements on the same index that overlap in time raise a lint warning.
data-media-start	No	Offset into the media source, in seconds.
data-volume	No	Static audio gain, default 1 (0 dB). 0 is silence and values above 1 boost, up to 3.98 (+12 dB) — Studio's fader writes this. For fades and ducking, use the data-automation volume lane (see creator-editing-recipes.md).
data-has-audio	No (<video> only)	"true" to declare the video carries an audio track when auto-detection would miss it.

The visibility window is half-open: [start, start + duration). A clip shows while start ≤ t < start + duration and is hidden at exactly t = start + duration. Land an animation's resolved end state slightly before data-duration, not on it, or its last frame is never rendered. Two clips can therefore be authored back to back (b.start === a.start + a.duration) with no overlapping frame.

Root-level clips get automatic layout. For direct children of the composition root that carry data-start, the runtime forces position: absolute and anchors them at top: 0; left: 0, sizing them to 100% when they have no computed size, so scenes stack in the same viewport layer. Elements without data-start are skipped entirely: an untimed full-bleed background needs its own position: absolute; inset: 0, or it collapses to zero height.

Sub-Composition Host Attributes

When a clip is a sub-composition host (loads another composition file):

Attribute	Required	Meaning
data-composition-id	Recommended	The composition ID of the loaded file. Matching it is the convention; a host that names a different id, or none at all, is supported but resolves silently.
data-composition-src	Yes	Path to the sub-composition HTML file.
data-width / data-height	No	Render dimensions for the instance. The compiler backfills them from the loaded file's root when absent.
data-variable-values	No	Per-instance variable overrides as JSON. See variables-and-media.md.
data-var-src	No	Binds the element's src to a declared variable id (media/image substitution, authored src = fallback).
data-var-text	No	Binds the element's own text to a scalar variable id; children are preserved.

See sub-compositions.md for the full wiring pattern.

Authoring Hints

• id="root" — template convention used by scaffolds and the transition catalog so CSS can target the composition root with #root instead of [data-composition-id="main"]. Not required by the runtime, but consistent with the rest of the ecosystem.
• class="clip": layout and tooling convention on visible timed elements (<div>, <img>, …), not a runtime requirement. See Clip Attributes above.
• data-root="true": names the composition root explicitly. Without it the runtime picks the outermost [data-composition-id] element, which is right for almost every file; set it when compositions nest and you need to be unambiguous.
• data-layout-allow-overflow — tells hyperframes check that overflow on this element (or its descendants) is intentional. Notes:
  • The check layout audit measures getBoundingClientRect at sampled timestamps, not rendered pixels. overflow: hidden clips the visual but does not suppress a layout finding. This attribute is the escape hatch; CSS overflow is not.
  • Can be set on the composition root as well as on any child. When the cited offender is div.<comp>-root inside div.<comp>-root (the root reports its own children's union as overflowing), the fix goes on the root, not on individual text descendants — shrinking font sizes will not converge.
  • In a multi-scene group_wN.html (continue runs), every scene-local element stays in the DOM during the other scenes' time windows; the layout-box union almost always overflows the canvas during morph seams. Mark the root and every scene-local primary/supporting element with this attribute at construction, not after check flags it.
  • Blast radius — it silences more than the overflow audit. The attribute is inherited down the subtree (the perception probe walks ancestors), so it also suppresses the rendered-perception checks text-clipping, content-cramped-container, and foreground-over-panel for every descendant. Putting it on a persistent panel that also hosts real foreground content disables collision checks on that content for the panel's whole lifetime. Prefer the narrowest opt-out: scope it to the smallest decorative wrapper, or use per-element data-layout-bleed="true" for one intentional primary-text crop. The two canvas/edge checks primary-offscreen and foreground-over-panel deliberately run even under allow-overflow, so it cannot hide a wordmark sliced by the frame or text bleeding onto a panel edge.
• data-layout-ignore — exclude this element from layout audits entirely.
• data-layout-allow-caption-zone — opt out of --caption-zone / caption_zone_collision for intentional lower-third copy (applies to the element and every descendant via closest; does not suppress overflow, overlap, occlusion, or other layout audits — pair those attrs if needed).

Legacy / Removed Attributes

These names appear in older projects and examples. Use the current names when authoring or editing:

Legacy name	Use instead
data-layer	data-track-index
data-end	data-duration