What is window focus?
The keyboard can only be used to “type into” one X client at a time. The mouse is used to determine which client has “focus”, or recives keyboard events. There are two major kinds of focus, “pointer” and “explicit”. Pointer focus, also known as “focus-follows-mouse”, means that wherever the mouse cursor is, that window has focus. Explicit focus, or “click-to-type”, means that a mouse button (usually the first, or leftmost on a right-handed mouse) must be clicked on a window with the mouse pointer over it for focus to change to that window. The focus policies available are determined by the window manager. Traditionally, pointer focus, or something very similar, is used in the X Window System — but there is no reason explicit focus cannot be used, and X clients work equally well with either focus policy.
