The perl/TK FAQ at http://www.cpan.org/authors/id/C/CL/CLAIRD/ptkFAQ.html is pretty useful for figuring out some of the more obscure options/widgets. The 'widget' demo program that ichipmunki mentioned, and which comes with the module (so you probably already have it) is also nice for finding code that does what you want. It also lets you view it's sample code from within the program and change it on the fly to see what your changes do.
I hope this helps.

sm3g
perl -e 's;;uoli;;$a=length;y;g-w;e-u;;;$a--;s;j;$a;;print"$_\n";'