What exactly is meant by the word "kind" here when you say kind-specific vectors?

If I have `function X(a) { this.a = a; }` and then `function Y(b) { this.b = b; }` does that mean `new X(1)` and `new Y(2)` are considered objects of different kinds?

And what about creating objects with literals: are `{a: 1}` and `{b: 2}` considered objects of different kinds?

They're specification wise, statically separate kind of objects: A class constructor is special and requires more "internal slots" so they live in their own vector, as do ArrayBuffers, TypedArrays, Arrays, DataViews, Maps, Sets, ...

But objects that have different shapes do not end up in their own vectors, since the shape is a dynamic property.