PHP is a widely-used general-purpose scripting language that is especially suited for Web development and can be embedded into HTML.

If you write in a PHP.net URL, like http://www.php.net/links, first this URL is matched against the PHP.net pages. If there is a page named links.php, then you'll get that page immediately. This type of shortcut makes easy to type in a link in an IRC conversation or mailing list message. If the script finds no page with this name, it tries to find a manual page.
Manual shortcuts

If your URL can't be matched with a page name, a manual page is searched for your query. This is the case for the http://www.php.net/preg_match URL. The following pages are searched for in the manual:

* Chapter pages, like http://www.php.net/installation
* Reference pages, like http://www.php.net/imap
* Function pages, like http://www.php.net/join
* Class pages, like http://www.php.net/dir
* Feature pages, like http://www.php.net/safe_mode
* Control structure pages, like http://www.php.net/while
* Other language pages, like http://www.php.net/oop

At last, if there is no PHP page, and there is no manual page matching your query, a search is issued on the site with the query you typed into the URL. An example of this kind of URL is http://www.php.net/search_for_this. The exact behaviour of this search is affected by your own My PHP.net settings.