Comment programming, also known as comment-driven development (CDD) is a software development technique that is based on the regular use of comment tags. In comment programming the comment tags are not used to describe what a certain piece of code is doing, but rather to stop some parts of the code from being executed. The aim is to have the commented code at the developer's disposal at any time he might need it. This is especially useful when the requirements change rapidly. In this case they happen to revert to older versions of themselves, thus making the programmer either write the code again, or revert parts of the code from the versioning repository, which would be more time-consuming. With comment programming, when such a request for reverting to an old implementation arises, the developer just comments the current implementation and uncomments the previous. It is advisable to add short descriptive comments to blocks of commented code.