Sloan, this has to do with the appearance of cross cut sails, made with two sail cloth materials, technically not in compliance with rule G.3.4.b specifying uniformity of legal sail cloth material. (Personally I am not sure why there is such as fuss over uniform cloth, so long as the cloth is legal, but so be it.

The absolute definition of the rule makes all spinnakers similarly illegal. Why? As specified by the strictest definition of the rules, all F18 Spis include reinforcing cloth at the grommets, and therefore, are technically constructed out of two dissimilar sail cloths.

If the clarification of the rule is anything like other recent decisions, the outcome may be more murky after the necessary ruling discussion that will be forthcoming...If they aren't the most clear, at least, our ruling body is amusing!