Focus follows mouse

Two answers exist to the question of which window the keyboard is talking to. Under click to focus, the window you last clicked, and it stays that way however far the pointer wanders. Under focus follows mouse, whichever window the pointer happens to be over, decided continuously and without any click at all. The second is the older answer, inherited from the X Window System, and it survives as an option in most Unix desktops and in nothing else at all. The variant most people actually run is the forgiving one, often called sloppy focus, where focus stays with the last window the pointer entered instead of evaporating when it strays onto the background.

What its defenders like is that pointing and focusing stop being two separate acts. Glance at a terminal behind your editor, move the pointer, type, and the command runs without the window ever coming to the front or the editor losing its scroll position. For anyone working across several windows at once, that is a real saving, and it is why the setting has outlived the desktop metaphor that produced it. What its detractors point out is that the pointer has quietly become a mode with no indicator: a nudge of the mouse, a palm on a trackpad, or an animation sliding a window under the cursor can redirect a password into the wrong window, and nothing about the screen says so until afterwards. Both camps are describing the same mechanism accurately. It is a preference, not a mistake.

The web has none of it. A browser is click to focus, and inside a page focus is claimed by a click or by Tab and by nothing else. What the web offers instead is hover, which is deliberately a separate channel: hover says the pointer is here, focus says the keyboard is here, and a page that wires the first to the second breaks assistive technology, steals keystrokes from anyone who is typing, and produces the notorious hover trap where a menu opens under a pointer that was only passing through. This is why focus visible exists as its own state and why sticky hover is a bug worth naming.

The practical rule is that this belongs to the window manager and stops there. Read it as vocabulary for arguing about desktop configuration, and as a useful reminder of what a focus model is: a policy about where typed characters go, chosen once for a whole system, rather than anything an individual interface gets to decide for its own components.