diff --git a/spec/README.md b/spec/README.md
index 8efd004..cc6c04b 100644
--- a/spec/README.md
+++ b/spec/README.md
@@ -15,3 +15,4 @@ Options are:
 
 ## manifest format
 
+TODO: document the old bsd, new bsd, and the extensions done in go-mtree