Here is the translation of your text into English, including the explanation of the PHP code:
---
Several functions in PHP for obtaining file paths:
Code as follows:
```php
"; // Get the server document root
echo $_SERVER['PHP_SELF'].""; // Get the absolute server path of the file executing this code
echo __FILE__.""; // Get the absolute file system path of the file
echo dirname(__FILE__); // Get the directory path where the file resides
?>
```
### Explanation of the Code:
1. **`$_SERVER['DOCUMENT_ROOT']`**: Retrieves the root directory of the server's document (the web root).
2. **`$_SERVER['PHP_SELF']`**: Retrieves the absolute server path of the file that is currently executing this code.
3. **`__FILE__`**: Retrieves the absolute file system path of the current file.
4. **`dirname(__FILE__)`**: Retrieves the directory path where the current file resides.
Let me know if you need further clarification!