http://www.purl.org/tcl/home/man/tcl8.4/TkCmd/frame.htm
Jeffrey Hobbs has written, "The whole container/use idea is nice, but was only pushed far enough to enable embedding Tk into Netscape/IE. There are definite problems with handling focus and message passing ..."
So I guess it is up to the Tk community to jump in and improve this capability?
Tk syntax help - Arts and crafts of Tcl-Tk programming - Category Command in the Tk package.