Utility procedures for managing the input focus.
http://purl.org/tcl/home/man/tcl8.4/TkCmd/focusNext.htm
See also: focusNext.
SYNOPSIS
tk_focusNext window
DESCRIPTION
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.
When would one most likely use tk_focusNext - in the context of writing bind commands?
See also:
Tk syntax help - Arts and Crafts of Tcl-Tk Programming - Category Command, part of the Tk package.