All the monks who answered, regularly read all daily posts at perlmonks, and the newsgroup comp.lang.perl.tk, and save good examples which we see. These questions come up so often, that we have a good collection of scripts which we can use to impress new users. :-) But we have no special powers, just tedious methodical study day after day. You can do it too. Often, if you know the right words to google for, you can go to groups.google.com and search comp.lang.perl.misc or comp.lang.perl.tk and search for answers yourself. For instance, for your question you might search for "entry focus" and/or "entry validate", and you will find most of the code which we have shown ( or close).