There are many different autoloader recommendations in PHP land. The one we will be using to modernize our legacy application is based on something called PSR-0
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PSR-0 is a PHP Framework Interoperability Group recommendation for structuring your class files. The recommendation rises out of a long history of projects using the "class-to-file" naming convention from the days of PHP 4. Originating with Horde and PEAR, the convention was adopted by early PHP 5 projects such as Solar and Zend Framework, and later by projects such as Symfony2.
We use PSR-0 instead of the newer PSR-4 recommendation because we are dealing with legacy code, code that was probably developed before PHP 5.3 namespaces came into being. Code written before PHP 5.3 did not have access to namespace separators, so authors following the class-to-file naming convention would typically use underscores in class names as a pseudo-namespace separator. PSR-0 makes an allowance for older non-PHP-5.3 pseudo-namespaces, making...