PHP __file__ __dir__ Magic constants using "PHP Advanced Tutorial"

<?php
$dir = dirname (__file__);
?>
in PHP5.3, a new constant __dir__ is added, pointing to the directory where the PHP script is currently executing.
For example, the currently executing PHP file is/www/website/index.php
then __file__ equals '/www/website/index.php '
and __dir__ equals '/www/website '
now we want to include the files in the current file directory or subdirectories, which can be used directly:
<?php
require_once __dir__. '/path/to/test.inc.php ';
?>

PHP __file__ __dir__ Magic constants using "PHP Advanced Tutorial"