[Retr0id]

An encoder should try to avoid them, but in theory it doesn't have to, right?

[lifthrasiir]

Yeah, it's not mandatory. The specification itself recommends a very concrete algorithm though, and one of its criteria is literally the average density [1].

[1] https://github.com/lifthrasiir/qr.js/blob/52f0409a22c5ece6a5...