diff --git a/tilesets.md b/tilesets.md
index f1389d4..bce5e3a 100644
--- a/tilesets.md
+++ b/tilesets.md
@@ -43,4 +43,18 @@ Aquaria will first search for the graphic name in your mod (under **graphics/...
 
 You can use your own numbering. More precisely, there can be holes in your numbering.
 This is useful if you want to categorize tiles for faster access in the editor. You could for example use 10-50 for rock tiles, 50-100 for plants, 100-150 for other decoration; and fill those slots over time while you add new tiles. You'll get a feel for this when you repeatedly cycle through tiles in the editor.
-Just don't use the same number twice.
+
+### Tileset rules:
+
+- IDs don't need to be sorted, but it's recommended since it avoids turning the tileset into a mess.
+- Don't use the same ID more than once.
+- IDs don't need to be contiguous. Holes are fine.
+- Don't change IDs for no reason. Tiles on the map reference tiles in the tileset by ID.
+  - If you do this, tiles on the map will change textures because the IDs desync.
+  - However, this makes it very easy to change a tile texture map-wide if you need to. Keep the ID, change the texture, done.
+- Tilesets can use up to ID 1023. IDs >= 1024 are reserved for Aquarian letter tiles.
+
+### Compatibility Notes:
+
+- Pre-OSE versions always load all tiles from the tileset into memory upon loading a map. This increases loading time and wastes RAM if your tileset contains a lot of tiles but your map doesn't use all of them.
+- Newer versions only load new tiles when the tileset changes, and only the tiles that are actually needed.