The attribute is in the HTML schema reference and enforced by the missing_data_no_timeline lint rule, but no page said what omitting it costs: a composition that never registers a GSAP timeline waits out player-ready-timeout (45 s by default) on every render.
That matters for triage because it is a fixed cost. "The render is slow" currently lists only causes that scale with the project - draft quality, media size, filter complexity - so an author whose renders are uniformly 45 s long reads the section, tunes the things it names, and sees no change.
- troubleshooting: add a symptom-keyed entry above "The render is slow", and point that section at it for the constant-penalty case.
- html-schema: give the attribute row the consequence and the lint code.
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>