tk_focusNext man page
tk_focusNext, tk_focusPrev, tk_focusFollowsMouse — Utility procedures for managing the input focus.
tk_focusNext is a utility procedure used for keyboard traversal. It returns the “next” window after window in focus order. The focus order is determined by the stacking order of windows and the structure of the window hierarchy. Among siblings, the focus order is the same as the stacking order, with the lowest window being first. If a window has children, the window is visited first, followed by its children (recursively), followed by its next sibling. Top-level windows other than window are skipped, so that tk_focusNext never returns a window in a different top-level from window.
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: 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.
focus, keyboard traversal, top-level
The man pages tk_focusFollowsMouse(n) and tk_focusPrev(n) are aliases of tk_focusNext(n).