"Infinite recursion is prevented. Any frame that attempts to assign as its SRC a URL used by any of its ancestors is treated as if it has no SRC URL at all (basically a blank frame). This doesn't prevent all malicious documents, but it eliminates a troublesome class of them."

Ah well, probably for the best really... It seems to have a recursion limit of 10 on Firefox, and 12 on Chrome.

I cheated by creating your original frameset pattern and then just recursing index.html in the middle frame. It improves the recursion effect a bit, but still isn't infinite.

http://downloads.intermer.net/frames/