A popover must not cover the control that opened it
Aliases: occluded trigger · covered opener · hidden anchor
What it is
While a popover is open, the control that summoned it should remain visible. Not occluding the trigger lets people match “which one I opened” with the content in the layer, and tap the trigger again to close. If the layer covers its own button, the ownership cue is eaten by the layer, and close often turns into tapping at guesses. This is not flipping: flipping keeps the whole layer visible; this keeps the origin visible. When they fight, a visible origin outranks preferred direction.
Why it happens
Anchoring runs on adjacency, and adjacency needs both sides present. Once the trigger is covered, adjacency becomes “there is probably a button under the layer,” and spatial ownership is memory. In a row of identical buttons, memory soon pins the layer to the neighbour. The trigger also often owns close: tap it again and the layer goes. Covered, that tap lands on the layer — it may choose an item, it may do nothing, it will not close. An arrow drawn on the layer and pointing at a covered blank also loses its referent. Flipping to the other side usually yields the trigger; if every direction covers it (the layer is too large), shrink the layer or change container rather than accept a missing origin.
Studying it
After open, measure exposed pixels of the trigger, whether a second tap on the trigger closes, and misattribution in a button row. Independent variables: layer size, whether the preferred direction covers the trigger, whether flipping may change direction to yield the trigger. Dependent variables: visible trigger area, success of toggle-close, ownership errors. With flipping forbidden and the layer expanding over the trigger, close success should drop.
Where it stops holding
A full-width action sheet does not declare ownership by sitting next to a button; a covered trigger is a different structure and is not judged by this popover rule. A tooltip almost always avoids its trigger, but a tooltip is not a popover. When the trigger is a long field and the layer opens from its lower edge, the field remaining visible is not occlusion; if the layer flips up and covers the typed value being compared, it is. Brief overlap during motion can be tolerated; the resting state cannot.
Applying it
- Treat the trigger rectangle as a no-cover zone in collision, and prefer a direction that does not intersect it.
- Keep tap-again-to-close; that tap must not land on an item in the layer.
- If the layer is large enough that every direction covers the trigger, shrink the content or change container rather than hide the origin.
- How to check: screenshot the resting layer; the trigger should be fully visible. A second tap on it should close the layer, not activate the first item inside.