In plain English
When a keyboard user Tabs onto something, that is like hovering, not clicking. It should be safe. This rule says the mere act of focusing an element must not set off a surprise: no popup opening, no jumping to a new page, no focus flying off somewhere else.
Changes like that are fine when someone deliberately activates a control (clicks it or presses Enter). They are not fine just because focus arrived.
Who this is for
- Keyboard users, who move focus constantly and cannot predict surprises.
- Screen-reader users, who get disoriented when the page changes under them without an action.
- People with cognitive differences, for whom unexpected changes are especially disruptive.
What “good” looks like
Wait for a real action before changing context.
Tab onto a "country" dropdown → nothing happens yet. ✓
Choose a country and press Enter (or click Apply) → updates. ✓
Tab onto the dropdown → page instantly reloads. ✗Where stores get it wrong
Auto-submitting select menus that navigate on focus, fields that trigger modals when tabbed into, and widgets that steal focus on load. These predictability problems appear on the common failures list.