Other gestures must be suppressed during fine control

What it is

Once a caret drag, handle drag, or space-bar slide has started, later displacement of that same finger must keep serving that job. If scroll, back, keyboard dismiss, or a system edge gesture inserts itself, the nudge is cut, the selection or caret stops halfway, or the whole page is swept away. During fine control, gestures that would steal the same contact stream must be suppressed.

Why it happens

Several recognisers watch the contact stream in parallel: scroll wants speed and direction, back wants an edge origin, keyboard dismiss may watch a downward swipe, caret drag wants horizontal displacement. Without exclusivity, a slightly vertical bias hits the scroll threshold, the page carries the target gap away, and the magnifier faces empty space. Space-bar sliding is more fragile: space is a key, so a recogniser must threshold “still a space tap” against “already a trackpad”; if another gesture (two-finger, edge) is satisfied in that window, the mode jumps away. Suppression is not turning those gestures off forever. It hands the contact to the nudge recogniser from “fine control confirmed” until lift. Outside that window they work as usual. Failures are concrete: the page jumps mid-drag, the keyboard dismisses, or system back closes the editor.

Studying it

During a nudge, inject confusable displacement (slightly vertical, near an edge, across space). Log which recogniser wins and whether the task is interrupted. Independent variables include scroll threshold, edge reserve, and space-slide start distance; dependent measures include false scroll/back/dismiss and the fraction of nudges completed. Horizontal drags in the middle of the screen hide the conflict.

Where it stops holding

A long document that must be scrolled while watching cannot lock scroll completely; the right split is one finger keeps nudging, two fingers or a scroll gesture open another channel. Assistive-technology system gestures must sometimes interrupt and must not be swallowed by the app. Mouse drag-select uses button state rather than gesture recognisers; the suppression set differs.

Applying it

• After a caret or handle drag starts, do not award that same contact to scroll, edge-back, or keyboard dismiss until lift.
• Give space-bar sliding a clear start distance, then exclusive control; a light tap before that distance remains a space.
• Drag the caret once from the bottom edge and once from mid-text; if either becomes system back or list scroll, the suppression window does not yet cover that path.

Related

• Same group: C6.14.1 The magnifier solves occlusion, not precision · C6.14.2 Indirect nudges such as sliding on the space bar beat direct dragging
• Adjacent: C3.19 Gesture conflicts and disambiguation · C6.13 Text selection and caret placement
• Search: gesture conflict · exclusive recognizer · caret drag