Manual:$wgAutoloadClasses

Details
Array mapping class names or interface names to filenames, for autoloading.

Example
Extension NewExtension is being implemented. The extension files are saved in the directory NewExtension, which is located in the extensions directory of the MediaWiki installation.

NewExtension is introducing a new class called NewClass, which is contained in the file NewClass.php

The proper settings for $wgAutoloadClasses is as follows: