Wulf Ratbane said:Or at the very least, it's derivable from Open Content.
You skipped that part.
Well, I imagine that it is derived from the 3.5 PHB, not the 3.5 SRD. The 3.5 PHB is all closed. It does happen to have very similar material to the 3.5 SRD, though.
You could, in theory, do the same thing - "derive" a 4E from the 3.5 SRD. But the 4E PHB etc. will not be open content. The 4E SRD will be, but a different type of open content, under a different, but similarly named license.