__file__ PHP Parsing

Today, I met the question of PHP's constant __file__.
Looked it up on the Internet. The following rules are summarized.
The dirname (__file___) function returns the path where the script is located.
For example, the file b.php contains the following content:
<?php
$basedir = DirName (__file__);
?>
If b.php is referenced by a a.php file require or include in another directory.
The contents of the variable $basedir are also the path to the folder where the b.php resides.
Instead of becoming the directory where the a.php file resides.
DirName (__file__) typically returns a directory structure of the current directory of the file to the system root directory.
The current file name is not returned.
DirName (__file__) may also return one. (current directory)
[The reason is that the b.php file is under the default Web directory of the http.conf or PHP Configuration development environment.]
For example web_root: "c:/root/www/".
The b.php file path is: "c:/root/www/b.php".

Using the method tips,
If you repeat, you can raise the directory up one level:
For example: $d = DirName (dirname (__file__));
The fact is that a directory to dirname () to do the parameters. Because DirName () returns the final directory without \ \ or
So when you reuse it, you can think of dirname () handling the lowest-level directory as a file name. Return as usual
The parent directory of the current directory. That way, you get the top level of the directory.

Files that contain the previous level of the directory
Include (DirName (__file__). ' /.. /filename.php ');

__file__ PHP Parsing