Copy paste from article on devzone: Allow toggling error suppression. We feel -- and the greater PHP community does as well -- that error suppression is a bad idea. It's expensive, and it masks very real application problems. So, by default, we want it off. However, if a developer insists that it be on, we should allow toggling it on.

Copy paste from docs: By default, Zend_Loader_Autoloader does no error suppression when using its internal autoloader, which utilizes Zend_Loader::loadClass(). Most of the time, this is exactly what you want. However, there may be cases where you want to suppress them. You can do this using suppressNotFoundWarnings():

Autoloader.php line 78. protected $_suppressNotFoundWarnings = true;