This form of documentation is key. In our experience, other forms of documentation invariably become out-of-date. How many times have you been asked to make a change to someone else�s code? Do you trust the documentation, or do you review the comments and the code itself to find �the truth�? High-quality module and subroutine headers, excellent block and in-line comments, and good naming conventions are the best types of documentation possible. At TMS, we have tools that build �documentation� from the source files�it�s a good test of the standard of commenting.