Bukkit/CraftBukkit — comment on commit 710f63b83f29bbd6ee9089d049152e2cba1e43d7
File: src/main/java/net/minecraft/server/World.java line 886
By xZise:

Wouldn't be more straight forward if each `SpawnReason` value has a boolean if it is `natural` (and will be canceled if not allowed) and simply check `spawnReason.isNatural()`? So if new reasons come up, you only have to add the reason.

Fabian