I will be adding some more options to the birthdate calculator to customise the computation and the output format. Users will need a way to save these options from visit to visit.

I could create a login system with accounts and passwords and option menus and… or maybe not. This is just for fun! Life shouldn’t need a login!

So, if you hit the “save options” button, the page takes the current settings, and embeds them in the URL shown in the browser URL bar. Nothing else happens. If you then bookmark that new URL, and use it to return to the page later, you’ll get the same settings back again. You can also copy the URL and send it to someone else, or put it as a link in a webpage, and others will be able to visit the page with the same settings too. No logins, no passwords, no fuss.