I need a little clearing up on Containers

I’m new to the Slim Framwork, am reading through the UserGuide, downloaded Slim Skeleton (as suggested in the tutorial), looked through the vendor folder and saw there container-interop and pimple (among other things).

So what I want to know is why they both are there. Pimple is a DI container and container-interop is “just” a container? Pimple does not require container-interop (according to it’s composer.json).
Is Slim itself using container-interop for something else internally?

If someone could clear this out for me, that would be nice.

container-interop provides an interface which Pimple, and many other DI packages, implement. This makes it easier if you start a project with one container, say Pimple, and then decide to switch and use a different container. Since your project depends on the implementation, rather than the specific container, you can swap with minimal fuss.

Alright, that makes sence. Thanks.