I'm just starting to learn nix and I found it confusing that import <nixpkgs> appears in many examples, yet the angle bracket syntax is not mentioned in the nix expression syntax documentation. I did end up finding an explanation for it in the "Common environment variables" section, but I think it the syntax should be documented with the rest of the syntax documentation.

EDIT:
I would add the documentation myself, but I actually don't feel that I fully understand the angle bracket syntax from reading the explanation in "Common environment variables".