I'm a bit confused by this. `showTooltip` creates a new Tooltip, but `removeVisibleTooltip` never actually deletes the old one, it just calls `stop`, which in turn hides it.

Why are we creating a new Tooltip here, and not inside a hidden/protected constructor function? Is this some other way of doing singletons that I've forgotten/don't know about? Or is the code convention just to only call showTooltip once per page?