Utility procedures for managing the input focus.
http://purl.org/tcl/home/man/tcl8.4/TkCmd/focusNext.htm
See also: focusPrev.
SYNOPSIS
tk_focusPrev window
DESCRIPTION
tk_focusPrev is similar to 'tk_focusNext except that it returns the window just before window in the focus order.
See also:
Tk syntax help - Arts and Crafts of Tcl-Tk Programming - Category Command, part of the Tk package.