How to create an anchored group?

I can make an anchored text frame:

myAnchoredFrame = myInsertionPoint.textFrames.add();

I can create a group on a page:

myPage.groups.add();

But I cannot create an anchored group!

myAnchoredGroup = myInsertionPoint.groups.add();

Result: "myInsertionPoint.groups.add() is not a function".

I've had to resort to app.cut() and app.paste().

But I'd like to know how to do this properly next time.

If anyone knows how to do this, it would be much appreciated.