Adds some explanatory javadocs and check world in ModelDataManager (#5762)

src/main/java/net/minecraftforge/client/model/ModelDataManager.java

@@ -108,6 +108,7 @@ public class ModelDataManager
     
     public static Map<BlockPos, IModelData> getModelData(World world, ChunkPos pos)
     {
+        Preconditions.checkArgument(world.isRemote, "Asked ModelDataManager from server world!");
         refreshModelData(world, pos);
         return modelDataCache.getOrDefault(pos, Collections.emptyMap());
     }

src/main/java/net/minecraftforge/common/extensions/IForgeTileEntity.java

@@ -172,6 +172,10 @@ public interface IForgeTileEntity extends ICapabilitySerializable<CompoundNBT>
          return false;
      }
 
+    /**
+     * Requests a refresh for the model data of your TE
+     * Call this every time your {@link #getModelData()} changes
+     */
      default void requestModelDataUpdate()
      {
          TileEntity te = getTileEntity();
@@ -182,6 +186,13 @@ public interface IForgeTileEntity extends ICapabilitySerializable<CompoundNBT>
          }
      }
 
+    /**
+     * Allows you to return additional model data.
+     * This data can be used to provide additional functionality in your {@link net.minecraft.client.renderer.model.IBakedModel}
+     * You need to schedule a refresh of you model data via {@link #requestModelDataUpdate()} if the result of this function changes.
+     * <b>Note that this method may be called on a chunk render thread instead of the main client thread</b>
+     * @return Your model data
+     */
      default @Nonnull IModelData getModelData()
      {
          return EmptyModelData.INSTANCE;