ClipMarkEvent
constClipMarkEvent:EventHandle<ClipMark,Local,Entity>
On an entity each time its one-shot clip crosses one of the marks
registerClip gave it, on the page that draws the clip: where a look
times its effect to the motion, with useClipMark. A local event: each
page emits its own as it animates, as each page plays the clip, and no
system reads it.