Rubber-banding at content bounds expresses the edge
Aliases: overscroll · rubber band · edge bounce
What it is
Surfaces have edges. After a pan has pushed the viewport to the end of the content, a hard lock leaves people unsure whether the gesture was ignored or there is simply no more. Rubber-banding (overscroll) lets the finger pull a little empty space past the bound, then springs back on lift. That space proves the edge. It is not another stretch of browsable content.
Why it happens
Inside the bound, tracking gain stays 1. Past it, gain drops quickly below 1 and displacement is crushed into a tightening elastic. The blank, shadow, or stretch encodes “this side is finished” as space rather than copy. Lift springs the overscroll back to zero. If gain stays 1 past the bound, people think there is more map. If displacement is forbidden entirely, the contact feels glued to a wall and is often reported as a freeze. The band must pull along the edge that was crossed; a diagonal corner pulls both.
Studying it
Have people pan past a known bound under hard clamp, rubber-band, and no feedback. Dependent measures include correctness of “is there more content,” repeated yanks on the bound, and time to return after lift. Measure the overscroll gain curve: too much residual motion looks like a newly loaded tile. Top-edge banding must be coded separately from pull-to-refresh, or one overscroll is claimed by two meanings.
Where it stops holding
A wrapping canvas or a globe has no longitudinal edge; forcing a band invents a fake wall near 180°. A snapping pager uses a detent spring at the page edge, not an end-of-content elastic; the feel is close but the meaning is “there is another detent,” not “there is no more.” When reduced-motion settings kill the band, a static edge shadow or a hard visual crop has to carry the bound signal.
Applying it
- Past the bound, drop tracking gain and show blank or an edge shadow; spring back on lift. Do not keep walking 1:1 in the overscroll direction.
- Split “no more” banding from “pull to load” in both threshold and look: the first returns home; the second arms refresh only after a second line.
- Have people push a map into the south-east corner and then push harder. They should see a gap and return to the corner on lift; if the picture never moves, they should still be able to say “that’s the edge.” Fail both and the bound was not expressed.