Implement tiled biome distribution

docs/PORTING.md

@@ -323,6 +323,12 @@ Overworld-like surfaces together with the persisted Native or Single biome
 distribution. This prevents Nether terrain generation from leaking into newly
 generated Cave Age chunks.
 
+Version 0.2.22.0 applies Tiled Biome Distribution using two deterministic
+Age-seeded biomes in the legacy diagonal-checkerboard layout. Each square is
+16 chunks (256 blocks) wide, matching Mystcraft Legacy's coordinate shift, and
+uses Minecraft's serializable checkerboard biome source so the layout remains
+stable across server reloads.
+
 Version 0.2.14.0 restores the legacy Linking and Descriptive Book artwork for
 inventory items and gives each book its matching open-book texture when placed
 on a Book Stand. Return Linking Books created inside another Age also retain and