Where are variables such as %2$s defined?

They’re placeholder/substitution variables. see https://www.php.net/manual/en/function.sprintf.php

I understand that they’re placeholders, but I can’t seem to figure out what variables are assigned to the placeholders.

— what for it… —

And know I’ve noticed, lol. The variables are in the widget’s constructor.

But thank-you for taking the time to reply esmi.