Sure, I understand these are just the steps to create a QR code and I could just Google why the QR code needs a masking pattern, but that’s besides the point. A good material would explain why I need it, instead of just saying it should be done. Even one sentence would be sufficient.
I found this pretty self-explanatory while just following the individual steps. However, a few sentences detailing the higher-level algorithm and its purpose right before the step which first introduces the masking pattern probably wouldn't be a bad idea either.
It turns out that you need a mask, otherwise you can too easily get a tag that is entirely (or close to) white or black. I was fortunate with a small code space (only 12 bit) that I could get away with a single mask, it never occurred to me that I could have used multiple masks (at the cost of a the bits to encode the choice)
I looks like extra complexity, but it solves a very pragmatic problem
In this case though, I chose to omit the why because other written resources on QR Codes have covered the topics extensively. Just to name a few: https://en.wikipedia.org/wiki/QR_code ; http://datagenetics.com/blog/november12013/index.html ; https://en.wikipedia.org/wiki/Error_correction_code#Interlea... ; https://en.wikipedia.org/wiki/Clock_recovery