Before version 4.3, the whole draw order is keyed as one. In 4.3+ you can key the whole draw order, or the order for a single folder. This allows you to compose draw order keys with a single animation or across multiple animations. For example, you might have a weapon that changes draw order (within a folder) and you can have that weapon in front or behind everything else (whole draw order).
Note meshes are not in the draw order, slots are. Also it doesn't make sense to think about draw order for a single slot on its own. The draw order is inherently about the relationship between multiple slots.
