Also, most windows aren't eligible for tooltips if they are not the focused, active window. I remember that difference being hard to explain to people when Windows 3.x and Mac Classic used entirely different title bars between the two states and sometimes even "shadowed" the window contents. It's especially hard to explain to today in a multi-monitor world and when inactive windows respond by default to all other inputs except some hover behaviors like tooltips. (I'm a software developer and know all this too well and I still tripped over it the other day wondering why tooltips wouldn't show up in a window and only realizing belatedly that the window wasn't active.)