How is PHP used to parse comments / headers for themes and plugins?

Question

Wordpress plugins and themes have comments like these at the top:

/**
 * @package Akismet
 */
/*
Plugin Name: Akismet
Plugin URI: http://akismet.com/?return=true
Description: Used by millions, Akismet is quite possibly the best way in the world to <strong>protect your blog from comment and trackback spam</strong>. It keeps your site protected from spam even while you sleep. To get started: 1) Click the "Activate" link to the left of this description, 2) <a href="http://akismet.com/get/?return=true">Sign up for an Akismet API key</a>, and 3) Go to your <a href="admin.php?page=akismet-key-config">Akismet configuration</a> page, and save your API key.
Version: 2.5.6
Author: Automattic
Author URI: http://automattic.com/wordpress-plugins/
License: GPLv2 or later
*/

And when you visit the plugins' page in the admin interface, the plugins are listed like this:

screenshot-with-shadow.png http://img854.imageshack.us/img854/4526/screenshotwithshadow.png

Is that a standard syntax for documentation? I'm assuming it does a file_get_contents on the plugin files to read them, but how does Wordpress parse that into manipulatable, standardized information to be used in PHP?

Answer 1

See get_plugin_data() in wp-admin/includes/plugin.php for the WordPress parser. More specifically the extraction happens in get_file_data() of wp-includes/functions.php:

function get_file_data( $file, $default_headers, $context = '' ) {
        // We don't need to write to the file, so just open for reading.
        $fp = fopen( $file, 'r' );

        // Pull only the first 8kiB of the file in.
        $file_data = fread( $fp, 8192 );

        // PHP will close file handle, but we are good citizens.
        fclose( $fp );

        // Make sure we catch CR-only line endings.
        $file_data = str_replace( "\r", "\n", $file_data );

        if ( $context && $extra_headers = apply_filters( "extra_{$context}_headers", array() ) ) {
                $extra_headers = array_combine( $extra_headers, $extra_headers ); // keys equal values
                $all_headers = array_merge( $extra_headers, (array) $default_headers );
        } else {
                $all_headers = $default_headers;
        }

        foreach ( $all_headers as $field => $regex ) {
                if ( preg_match( '/^[ \t\/*#@]*' . preg_quote( $regex, '/' ) . ':(.*)$/mi', $file_data, $match ) && $ma
                        $all_headers[ $field ] = _cleanup_header_comment( $match[1] );
                else
                        $all_headers[ $field ] = '';
        }

There are similar implementations outside of WP. See How can plugin systems be designed so they don't waste so many resources? for an example.