Sibling items yield to show the drop slot
Aliases: gap animation · drop slot · insertion gap
What it is
While a row is being carried, the other rows should open a gap that previews the insertion index. The drop location is not revealed at lift-off; neighbors continuously forecast it by moving aside. Without that yield, people guess between two frozen rows where the item will land.
Why it happens
Hit-testing maps the floating item’s midline or hotspot onto an insertion index. Rows on either side translate along the list axis, leaving a gap about as tall as the dragged row. The motion has to keep up with the finger without glittering. Yield is spatial prediction, not ornament: a gap is a cheaper anchor than rehearsing numeric indices. If only the grabbed row moves, the insertion index is an invisible state and a wrong drop is noticed only when the finger lifts.
Studying it
Record signed error between intended and released index, mid-drag corrections, and whether people can name the insertion slot before release. Factors include presence of yield, animation duration, variable row height, and an extra insertion line. Eye tracking shows whether gaze sits on the gap or on the floating row. Final order alone is a weak measure—correct results can be lucky after several failed drops.
Where it stops holding
Grid reorder yields in two dimensions, including wrap-around at line ends; a vertical list’s “push apart” does not transfer. Cross-section drags need a group-level accept state, because empty and full sections do not yield the same way. Reduced-motion settings can replace displacement with a static insertion line. Very short lists gain less, but a forecast still beats none. Yield does not bring off-screen destinations into view.
Applying it
- Drive the insertion index from the dragged item’s midline and open an equal-height gap in about 100–200 ms; do not wait for lift-off to reflow.
- Size the gap to the live row height so a short item does not look jammed between tall neighbors.
- Pause users mid-drag and ask where the item will land; match the spoken index to the real one, and find frames where the gap lags the finger.