Add feature order cycle guide

src/guides/feature-order-cycle.md

@@ -0,0 +1,76 @@
+---
+title: How to fix feature order cycles
+versions:
+  - '1.18'
+  - '1.18.2'
+  - '1.19'
+tags:
+  - worldgen
+  - biomes
+  - features
+---
+
+> java.lang.IllegalStateException: Feature order cycle found, involved biomes
+
+Are you getting this frustrating error? Let's look at why it happens and how to prevent it.
+
+## Why does it happen?
+Feature order cycles happen when two biomes reference the same placed feature in the same step, but in a different order.
+
+Let's try with an example. We have two biomes here:  
+**`data/example/worldgen/biome/forest.json`**
+```json
+{
+  ...
+  "features": [
+    [],
+    [
+      "example:blue_tree",
+      "example:red_tree",
+      "example:rocks",
+    ]
+  ]
+}
+```
+
+**`data/example/worldgen/biome/plains.json`**
+```json
+{
+  ...
+  "features": [
+    [
+      "example:blue_tree"
+    ],
+    [
+      "example:rocks",
+      "example:blue_tree"
+    ]
+  ]
+}
+```
+
+When we try to load these biomes, data pack validation will fail because in the `example:forest` biome in step 2, `blue_tree` is before `rocks`; while in the `example:plains` biome, `rocks` is before `blue_tree`.
+
+## How to fix it
+The rule is that for each step in `"features"`, all features need to be ordered consistently across biomes.
+
+The above example can be fixed by swapping the features in step 2 of the `plains` biome:  
+**`data/example/worldgen/biome/plains.json`**
+```json
+{
+  ...
+  "features": [
+    [
+      "example:blue_tree"
+    ],
+    [
+      "example:blue_tree",
+      "example:rocks"
+    ]
+  ]
+}
+```
+
+If your data pack is more complicated, with multiple biomes and lots of features, this will be a harder process. Since 1.18.2, the error will include the conflicting biome IDs.
+
+If you want more detailed errors, a useful mod is [Cyanide](https://www.curseforge.com/minecraft/mc-mods/cyanide-fabric). This will show the exact feature cycle that's causing problems, as well as other worldgen related errors.