Content on Hover or Focus
Where hover or focus triggers additional content to become visible, that content is dismissible without moving the pointer or focus, hoverable so the pointer can move over it without it disappearing, and persistent until dismissed or no longer relevant.
In plain language
If hovering or focusing on something makes extra content pop up (like a tooltip), that content must be possible to dismiss without moving away, possible to hover over without it disappearing, and it must stay visible long enough to actually read.
Why it matters
People with low vision often zoom in, meaning they may need to move their mouse toward a tooltip to read all of it — if it vanishes the moment they try, they can never read it. Others need extra time or a way to dismiss it, especially if it covers something important.
In practice
Fails this criterion
A tooltip appears when hovering over an icon, but disappears the instant the user tries to move their mouse toward it to read the full text.
Meets this criterion
The same tooltip stays visible when the user moves their mouse onto it, and can also be dismissed with the Escape key without needing to move the mouse away.
Test it yourself
Hover over or tab to anything that shows a tooltip or extra info. Try moving your mouse onto that new content, and try pressing Escape. If the content disappears before you can read it, or can't be dismissed without moving away, this criterion is failing.