When exporting grade level data, denote kindergarten with a number 0 (zero), not a letter K, and denote transitional kindergarten with -1 (negative one). What.

When exporting grade level data, denote kindergarten with a number 0 (zero), not a letter K, and denote transitional kindergarten with -1 (negative one). What. What on earth is this set of "guidelines". Is there a color scheme recommendation somewhere in here, too?