snap to start of preexisting stack.
snap to start of preexisting stack.

sclements/scratch-blocks,gengshenghong/scratch-blocks,LLK/scratch-blocks,LLK/scratch-blocks,griffpatch/scratch-blocks,griffpatch/scratch-blocks,gengshenghong/scratch-blocks,griffpatch/scratch-blocks,LLK/scratch-blocks,gengshenghong/scratch-blocks,gengshenghong/scratch-blocks,griffpatch/scratch-blocks,LLK/scratch-blocks,LLK/scratch-blocks,griffpatch/scratch-blocks,sclements/scratch-blocks,sclements/scratch-blocks,sclements/scratch-blocks,gengshenghong/scratch-blocks,sclements/scratch-blocks