lucy24 - 10:19 pm on Nov 16, 2012 (gmt 0)

Is the underlying structure "either all 5 members of group A are empty OR all 3 members of group B are empty"?

The [OR] operator only applies to pairs of adjoining lines. Or sets of adjoining lines if you string them together.

It's a pretty horrendous-looking rule no matter how you slice it ;) I hope you don't have to invoke it too often. Otherwise you might want to take some entirely different approach like detouring to a php script where you have benefit of grouping parentheses.