Function isTimedClipLeaf

packages/core/src/runtime/init.ts:1639–1645

(el: HTMLElement)

  // with `visibility:visible`), so containers keep that and only leaves leave-flow.
  let timedClipIsLeaf = new WeakMap<Element, boolean>();
  const isTimedClipLeaf = (el: HTMLElement): boolean => {
    const cached = timedClipIsLeaf.get(el);
    if (cached !== undefined) return cached;
    const leaf = el.querySelector("[data-start]") === null;
    timedClipIsLeaf.set(el, leaf);
    return leaf;
  };

  // Both caches key on live DOM facts that change when the timed-element set
  // changes: leaf status flips when a clip gains/loses a nested `[data-start]`