After computing the next window, tk_focusNext examines the window's -takefocus option to see whether it should be skipped. If so, tk_focusNext continues on to the next window in the focus order, until it eventually finds a window that will accept the focus or returns back to window.
tk_focusPrev is similar to tk_focusNext except that it returns the window just before window in the focus order.
tk_focusFollowsMouse changes the focus model for the application to an implicit one where the window under the mouse gets the focus. After this procedure is called, whenever the mouse enters a window Tk will automatically give it the input focus. The focus command may be used to move the focus to a window other than the one under the mouse, but as soon as the mouse moves into a new window the focus will jump to that window.
Note that at present there is no built-in support for returning the application to an explicit focus model; to do this you will have to write a script that deletes the bindings created by tk_focusFollowsMouse.