If you've ever tried to read code written by someone other than yourself (who hasn't?), you know it can be a daunting task. [...] PhpDoc, short for PhpDocumentor, is a powerful tool that allows you to easily document your code via specially formatted comments. [...] By using PhpDoc, you can make it easy for others (and yourself) to understand your code - weeks, months, and even years after you've written it.
He introduces the concept of "docblocks" and includes several examples of how to comment things like packages, files, classes and functions/methods. Finally, he wraps up the post with an example of using the "phpdoc" command to run phpDocumentor and build the docs. In the comments, another tool is also suggested - DocBlox, a project that still parses the same docbloc syntax but does it in a much more memory efficient way (and is an actively maintained project).