Hoverable, dismissible, persistent

This one is unusual: it is a term with no headword. Criterion 1.4.13 is called Content on Hover or Focus, but nobody says that out loud, and the three conditions it lists are always quoted together as a set, so the set became the name. Dismissible means there is a way to make the content go away without moving the pointer or the keyboard, which in practice means Escape. Hoverable means the pointer can travel onto the revealed content without it vanishing on the way. Persistent means it stays until the trigger is released, the reader dismisses it, or its information stops being true. Say all three, in that order, and everybody in the room knows exactly which rule you mean.

Each condition has its own signature bug. Hoverable fails when there is a gap between the trigger and the panel, because the pointer crosses that gap, the trigger’s hover ends, and the panel is gone before anybody reaches it. The fix has a nickname of its own, the hover bridge: a transparent strip covering the gap, or simply anchoring the panel flush against its trigger. Persistent fails to a timer, which usually looks reasonable to whoever wrote it and is punishing at four times magnification, where finding the panel and reading it can easily take longer than the timeout. Dismissible fails when the only way out is to move the mouse, which is no way out at all for somebody whose pointer is a head tracker or whose magnified viewport follows the caret.

The criterion applies to anything hover or focus reveals, which is a wider net than people expect. A tooltip is the obvious case. A hover card is the harder one, because it is bigger, it carries links, and being able to reach those links is precisely what hoverable is protecting. A popover opened by a click is outside the criterion on its trigger, but the moment it can also be opened by hover it is inside. Menus that open on hover are inside too.

Dismissible overlaps with light dismiss without being the same idea. Light dismiss is about clicking away from a surface to close it, and a pointer press is exactly what this criterion says must not be required. Escape is what satisfies both at once, which is why one keydown handler on the surface tends to be the whole repair. There are exceptions worth knowing: content that reports an input error, and content that obscures nothing, are excused from the dismissible condition, and content whose information has genuinely expired is allowed to leave on its own.