Though the invocation of this Tk command is tk_menuBar, it is documented as http://www.purl.org/tcl/home/man/tcl8.4/TkCmd/menubar.html .
See also incr Widgets doc. Here's an example of the Iwidgets menubar: http://204.247.240.249/iwidgets/iwidgets/menubar.html
Anyone have examples ?
Tk syntax help - Arts and crafts of Tcl-Tk programming - Category Command, a part of the Tk package