\Symfony\Component\DependencyInjection\ContainerInterface contains the following constants:

    const EXCEPTION_ON_INVALID_REFERENCE = 1;
    const NULL_ON_INVALID_REFERENCE = 2;
    const IGNORE_ON_INVALID_REFERENCE = 3;
    const IGNORE_ON_UNINITIALIZED_REFERENCE = 4;

The documentation for their usage with get() is nowhere to be found. I tried looking for their usage in the Symfony code, but deciphering what they precisely do (and what's the actual intention of using them) is rather hard.

Maybe we should document that?