I totally like `undefined` instead of `isUndefined` and `defined` instead of `isDefined`
But I think that the singular argument method should be different from the varargs argument method. 

My problem (except for the ambiguity earlier mentioned) with trying to combine the singular argument method call with varargs, is that varargs are really just an array passed to the method. If the singular argument method would be called with an array, that method would not perform a deep check for nullness, so why should the other one? Well, it makes sense if they're named differently.

So, as soon as we introduce varargs, there should be these four methods (as complement to the two with singular arg):
```
allDefined = !anyUndefined
anyDefined = !allUndefined
```

Otherwise, I'd suggest that we make the currently commented method recursive, and check for nullness on *all* members the full depth, even if I find it more than absurd that an array would be 'undefined' just because one of it's slots isn't filled.