How to make a QR code generater

QR codes are specified by the ISO/IEC 18004 standard, but if you can get your hands on a copy, you might be surprised that it describes irrelevant or possibly obselete functionalities. Despite that, 80% of it is still a great reference for building a generator. Fortunately, you have something even better. In this interactive text-based tutorial, I'll cover everything worth knowing and also point out some of the vestigial baggage that has survived since 1994.

A QR code needs to be read by a QR code scanner, so rather than the standard, our source of truth is scanner implementations, of which there are only ~3 that matter.