What problem does it solve? Building videos from HTML requires a strict contract so the renderer can seek frames deterministically; this Skill provides the structural rules, data attributes, and validation workflow needed to author compositions that render correctly. ## Core Features & Use Cases - Composition Contract: Defines root forms (standalone vs sub-composition), the data-* timing attributes, class="clip" visibility rules, tracks, and the single paused GSAP timeline registered on window.__timelines. - Determinism & Layout Rules: Enforces seekable, reproducible frames by banning render-time clocks, unseeded randomness, infinite repeats, and non-allowlisted animated properties. - Planning Formats & Validation: Documents STORYBOARD.md, BRIEF.md, and SCRIPT.md plan formats plus the npx hyperframes check / snapshot / render validation loop. - Use Case: When asked to build a 30-second product video as HTML, use this Skill to structure index.html with timed clips, sub-compositions per scene, and a registered timeline that passes lint and renders deterministically. ## Quick Start Read this skill before writing any composition HTML, then scaffold a minimal composition with a sized root, one clip, and a paused GSAP timeline registered under the composition id.