A non-modal panel lets the main surface keep running
Aliases: modeless panel · inspector beside content · parallel interaction
What it is
While a non-modal panel is open, the main surface can still scroll, select, and edit. The difference from a modal is not the silhouette. It is whether the main task keeps running: inspectors, outlines, and chat sidebars are legitimate because people change an object while watching the collection, or write while looking something up. If opening the panel locks the main surface, it is not non-modal — it is a dialog that forgot its scrim.
Why it happens
Parallel work needs two input channels alive. The panel spends a slice of attention; the main surface must still take pointer, keyboard, and selection changes so working memory can switch between “edit this bit” and “see the whole” without closing a door first. A modal cuts that switch and hangs one question at a time. Non-modality admits two questions can alternate if they act on the same in-progress work. In implementation the main surface must not be made inert, focus must not be trapped in the panel, and scroll and shortcuts must land on the layer actually in use. Which layer is in use is decided by the last click or focus, not by the panel’s existence. The moment the panel swallows main-surface clicks while open, the parallel contract has been quietly rewritten as modal.
Studying it
Open a sidebar on a main surface already being edited, and require a change on the main surface and a change in the panel without closing it. Record whether that is possible, misrouted clicks, and whether people feel locked. Independent variables: whether the panel traps focus, whether the main surface still scrolls. Dependent variables: success of alternating actions, time against a close-then-reopen baseline. If the panel must close before the main surface can change, it is modal in behaviour.
Where it stops holding
On a small touchscreen two live regions invite misses: parallel is physically true and precise-motion false, so the panel should become summonable rather than persistently parallel. A read-only preview is a safe parallel; a panel with a submit button can be read as submitting the main surface’s document, so the object of the action must be named. A screen reader speaks one region at a time, so “parallel” becomes “can move over”; landmarks have to cheapen that move, because visual side-by-side does not.
Applying it
- A click on the main surface while the panel is open should take effect there immediately, without closing the panel first.
- Do not put a full-screen scrim or a focus trap on a non-modal panel.
- Route shortcuts to the layer that currently has focus, and make both layers reachable from the keyboard.
- How to check: with the panel open, change three places on the main surface. If any change required a close, parallel operation does not hold.