PHP Manual: Register and return default file extensions for spl

string spl_autoload_extensions(stringnull $file_extensions = null)

This function can modify and check the file extensions that the built in __autoload fallback function spl_autoload will be using.

Note: There should not be a space between the defined file extensions.

file_extensions: If null, it simply returns the current list of extensions each separated by comma. To modify the list of file extensions, simply invoke the functions with the new list of file extensions to use in a single string with each extensions separated by comma.

A comma delimited list of default file extensions for spl_autoload.

Version	Description
8.0.0	`file_extensions` is now nullable.

Example #1 spl_autoload_extensions example

<?php
spl_autoload_extensions(".php,.inc");
?>