Book/article QR codes?

Question

QR codes

Tell me, please, what can I read in detail about QR codes, I'm interested in detailed materials (books, lessons)

Answer 1

Start with a Wikipedia article. See also the English version of the article. After that, if you still have questions and do not find answers from the links from the articles, clarify your question. And it's not even clear what to advise you. How it works. Applied or something.
For a programmer, for example, it is enough to know about ready-made libraries
phpqrcode.sourceforge.net - to draw it on the site
https://github.com/journeyapps/zxing-android-embedded - to read them from the phone
And what is encoded there as a string is already a separate question.
maybe a line like ?fn=....&tm=... something, invented for checks.
ST1 ...... - GOST is for payments.
banal
https://site.ru/
and came up with a lot of things.