I seem to recall first using the Widget Demo back in 1996 or 1997. It was written in a very early version of Perl5. [Disclaimer: This is my best recollection from about 15 years ago - corrections welcome.]

It served its purpose to demonstrate Perl/Tk widgets; I still refer to it occasionally.

I would not recommend this code for learning Perl today. Of course, if you click on the See Code button, you'll still need to understand it.

I do recommend the book Mastering Perl/Tk. (Just checked my copy - it was published in 2002 and uses Perl 5.6 - so, while it's a little more recent, I'd hardly call it modern.)