This would basically be a reverse crafting table, and the grid would look like a backwards crafting table grid. Let's use a Diamond Pickaxe as an example here. You would put the pickaxe in the first slot, and to the right of this slot is a 3x3 grid (like a crafting table) where the materials used to make the pickaxe will appear. Basically, what I'm trying to say is the Decrafter takes an already crafted item and breaks it down, and as a result, you get the materials that you used to make the original item back. I hoped I explained this well enough. This block would be essential for accidentally crafted items. Let's get this in a future update!