I, of course, agree with previous comments. And I remember folowing:
1/ The conditions expected for usual code execution should be specified (OS, memory, user, environment, ...)
2/ The documentation should contain an ideas. Ideas about WHY this code exists, HOW it resolves the problem and WHAT it expects and/or not expects - for instance, some code may expect that some combination of arguments cannot occur, because real world logic.
3/ The code should't be too clever ;) In other words, imho, I want to _read_ the code, I don't want be quizzed.