What's the Necessary Items to Document on code ?

Question

There is so many option in each programming languages which can be mentioned in the code documentation.

I want to know what are the most important Items which we have to document?

Answer 1

I'd document contracts (this parameter is expected not to be null, this function never returns null, ...) as well as the meaning (this method does that, ...). Besides documenting the API, I'd add comments on pieces of code which are non-trivial but add a significant value to the application (cryptic but real fast, works around a framework bug).

What you document ultimately depends a lor on who will read that documentation...