php - Load your custom classes in MODx Revolution -

i trying make simple class in modx getting 500 server error, ie example.

i created plugin , call on webpageinit

plugin

class foo {     function helloworld() {        echo 'hello world';     } }

and created snippet , try

snippet

$foo = new foo;

but getting internal server error 500, proper way this, or there autolader custom class?

i think documentation can give deeper explanation, making custom back-end programming.

Core code