Thanks, but I'm happy to be ignorant about levels three and four. I know they exist, and that's enough for me. Something is really wrong if programmers of most applications domains have to care about that complexity.
Knowing that their exist is the minimum you must know. Knowing what you don't know is already knowledge.
Joel gives the impression that he don't know that he don't know.
Knowing that you can't break a Unicode text string or insert text into the middle of Unicode string unless you know what language it uses is usually enough. They are just binary blocks you can't modify unless you have some extra info or uses specific libraries.
You have to know they exist, and know when you should worry about them (and call in to the appropriate APIs)
https://manishearth.github.io/blog/2017/01/15/breaking-our-l... gives an overview of most of the different things scripts do. Being aware of those helps a lot. It also gives a brief idea of how to deal with this stuff (usually it's just calling an API)
