`.selectedContainer` with non-collapsed selections

I think that it is better that you figure out [`makeTextSelection`'s signature](https://github.com/wymeditor/wymeditor/blob/3b3ec584e56e84b013117c107ae7594f7b954798/src/test/unit/utils.js#L305) instead. Which, is actually the way you guessed it.

That's just how we do things, don't we? We name variables after what they are—for example, a `p` element—not after what they are going to be in the called function. Usually, that is.

Calling the `p` element `p` here is very helpful, isn't it? And if you know the signature of `makeTextSelection`, then you know everything.