Updated to 1.21

remappedSrc/modern_chunk_detector/ModernChunkDetector.java

@@ -0,0 +1,22 @@
+package modern_chunk_detector;
+
+import net.fabricmc.api.ModInitializer;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class ModernChunkDetector implements ModInitializer {
+	// This logger is used to write text to the console and the log file.
+	// It is considered best practice to use your mod id as the logger's name.
+	// That way, it's clear which mod wrote info, warnings, and errors.
+    public static final Logger LOGGER = LoggerFactory.getLogger("modern_chunk_detector");
+
+	@Override
+	public void onInitialize() {
+		// This code runs as soon as Minecraft is in a mod-load-ready state.
+		// However, some things (like resources) may still be uninitialized.
+		// Proceed with mild caution.
+
+		LOGGER.info("Hello Fabric world!");
+	}
+}

remappedSrc/modern_chunk_detector/mixin/ExampleMixin.java

@@ -0,0 +1,15 @@
+package modern_chunk_detector.mixin;
+
+import net.minecraft.server.MinecraftServer;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+@Mixin(MinecraftServer.class)
+public class ExampleMixin {
+	@Inject(at = @At("HEAD"), method = "loadWorld")
+	private void init(CallbackInfo info) {
+		// This code is injected into the start of MinecraftServer.loadWorld()V
+	}
+}