Status Cycle
The phrase swaps on one clock while the shimmer runs on another. Two independent timers on the same element is what stops it looking like a single scripted loop.
Usage
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Meant for
Examples
On a Agent Status
One line of status replacing the next, with a shimmer running through whichever line is showing. The lines are stacked in one grid cell and each one's cycle starts a third of the loop later (negative delays, so all three are in step from the first frame), so the row never changes width.
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The class is wm wm-status-cycle — the first half is the marker the trigger and reduced-motion rules hook into, the second is the effect.