php function on php.net

Hi there, I am wondering how on php.net the search for functions is done. You can add any function just behind the php.net like php.net/phpinfo and it will point you right through it. I know how to redirect this as a 404 error in apache to another file, but then the url is changing. In the php.net case the url stayes the same. Does anybody know how this is done? Thanx, Merlin