Thanks for the replies, however neither is a solution to the problem. I want to make a seamless tessellation pattern using a clipping group as the unit of repetition. No matter what I try, Illustrator does not allow me to "over-ride" the anchor points of the clipping contents in order to snap the clipping path to grid. Of course it can be done manually, but if the clipping mask is an equilateral triangle, for example, and the pattern reflects on all sides of the triangle as it repeats, a manual construction is a hassle. And besides, the whole idea is to use snap-to-grid to guarantee a seamless tessellation.
The solution to the problem would be if Illustrator could treat a clipping path as a crop rather than a mask when snapping to grid.
