Perl can’t see the client side and HTML element ids are not part of the CGI/form specification so they aren’t sent with plain form submission; just input field name and value pairs.

It’s pretty easy to add information to form submissions with JavaScript and to do client side validation as well. You should note well however that client side validation is only for convenience and saving on traffic / server hits. You RFC:MUST validate the client data on the server as well. Circumventing client-side security is trivial for a hacker.

From your description, you’ll need JS. I personally recommend jQuery. You may not need Perl at all if you’re just talking to a bank’s API from the browser.