[miguel-heygen]

What

The variables page now says what can be a variable. It gains a plain-words table of the seven kinds, and a "Swap in a video or a sound" section: a link declared as a string and bound to a <video> or <audio> with data-var-src, the per-account example (render the same saved project once per account with --variables), and the limits.

Why

The page listed the kinds in a table of uses and never said that video and sound are links bound to a media element, what the render does with them, or where it stops.

Notes

• Docs only: docs/concepts/variables.mdx. No new page; the existing variables page already holds the kinds table, so the section sits beside it.
• The "length and sound follow the bound clip" paragraph describes the behaviour in fix(producer): render variable-bound media at the bound clip's length and loudness #7529. Merge after it.
• Limits written from the code: tags that accept data-var-src (VAR_SRC_TAGS, applyVariableBindings.ts), the URL gate (isSafeMediaUrl, compositionVariables.ts), nested mounts with their own data-variable-values resolved by the browser.

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[heygengenesis]

Request changes at acc4ba67. One blocker in the main example.

Blocker: the welcome-clip example doesn't swap the clip as written. The HTML is labelled compositions/welcome.html, but the command is a bare npx hyperframes render, which renders index.html (render.ts, --composition). That leaves two possible setups, and neither works:

• welcome.html isn't mounted from index.html, so it isn't rendered at all.
• welcome.html is mounted as a sub-composition. stashInstanceVariables (compositionLoader.ts) builds that scope from its declared defaults plus the host's data-variable-values only. --variables reaches it only as CSS custom properties, so data-var-src="welcomeClip" keeps the default. The #7529 pre-pass runs on the entry HTML before inlining, so it doesn't bind it either. The "length and sound follow the clip" paragraph then doesn't hold.

Fix either way:

• Label the block index.html, which matches the page's own "Override top-level values from the CLI".
• Or add --composition compositions/welcome.html to the command.

Nits:

• The URL-gate bullet says "a relative path or an http, https, or blob URL". Root-absolute paths (/clips/a.mp4) also pass, because isSafeMediaUrl accepts any value with no scheme. Maybe "a path, or an http/https/blob URL".
• The new ## What can be a variable sits inside "Advanced: declare the approved inputs". It turns the existing ### Say what a slot means into a child of it, so the outline reads oddly.

Everything else in the limits list matches the code: VAR_SRC_TAGS, a data: video being dropped with a warning, and nested data-variable-values mounts resolved by the browser.

[miguel-heygen]

Fixed at 8fd91d5: the example block is now labelled index.html (top-level, matching the page's CLI override section), the URL bullet says "a path or an http, https, or blob URL", and What can be a variable is now a ### under the Advanced section so Say what a slot means stays its sibling.

[heygengenesis]

Approve at 8fd91d50. No blockers. All three points from the earlier review are fixed, and nothing else changed:

• The example is now index.html. A bare npx hyperframes render uses it, and --variables welcomeClip goes through the top-level scope that #7529 binds before measuring. The "length and sound follow the clip" paragraph is now true for this setup.
• The URL bullet now says "a path", which matches isSafeMediaUrl (any value with no scheme passes).
• ### What can be a variable now sits under "Advanced: declare the approved inputs", so the outline reads cleanly. The cross-link to #swap-in-a-video-or-a-sound matches the heading.

The length/sound paragraph depends on #7529, which I approved at 364baab6. Keep the stated order: merge #7529 first.