PHP: URL Howto: This is a little known but great feature of the PHP Web site.
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.
Basically, they integrate the search string with the URL. Since PHP is a short URL, it’s easier just to rip off the url and search term together than click a bookmark and enter the search term in the box.