http://www.purl.org/tcl/home/man/tcl8.4/TkCmd/tkvars.html
The above page does not work. It yields the following message:
"The page you are looking for cannot be found.
Note: The site went through a fairly major overhaul in October, 2005. If you're looking for content that used to be here and can't find it, try using the "Search" box on each page..."
Tk syntax help - Arts and crafts of Tcl-Tk programming - Category Command