[WordPress] Using a PHP Autoloader in WordPress

00-autoloader.php

<?php

spl_autoload_register( 'acme_namespace_demo_autoload' );
/**
 * @param string $class_name The fully-qualified name of the class to load.
 */
function acme_namespace_demo_autoload( $class_name ) {

    // If the specified $class_name does not include our namespace, duck out.
    if ( false === strpos( $class_name, 'Acme_Namespace_Demo' ) ) {
        return;
    }
  
    // Autoloading work goes here...
  
}