Each file should start with a comment describing what the file does. For example:

<?php
// $Id: theme.inc,v 1.202 2004/07/08 16:08:21 dries Exp $

/**
 * @file
 * The theme system, which controls the output of Drupal.
 *
 * The theme system allows for nearly all output of the Drupal system to be
 * customized by user themes.
 */

The line immediately following the @file directive is a summary that will be shown in the list of all files in the generated documentation. If the line begins with a verb, that verb should be in present tense, e.g., "Handles file uploads." Further description may follow after a blank PHPDoc line.

In general, @file directives should not contain large descriptions, because those are better placed into @defgroup directives, so developers can look up high-level documentation by reading the "group" topic. See http://api.drupal.org/api/groups for a list of API topics/groups.

To add CVS ID-Tags to your file, add a // $Id$ to your file. CVS will automatically expand it to the format shown above. In the future, you don't have to care about that as CVS will update these information automatically.

For .install files, the following template is used:

/**
 * @file
 * Install, update and uninstall functions for the XXX module.
 */