http://purl.org/tcl/home/man/tcl8.4/TkCmd/menubutton.htm
[Anyone want to contribute some examples of how to use this, tips and tricks, etc.? ]
What do menubuttons offer that menubars don't? Chengye Mao observes that a "menubutton works in an embedded window and a menubar does not." Moreover, some situations (including use of icons rather than labels?) preclude use of native menubars.
Category Widget - Category Command - Tk syntax help - Arts and Crafts of Tcl-Tk Programming