diff --git a/core-principles/rules-for-extending.md b/core-principles/rules-for-extending.md
index 82e1253..4af97d9 100644
--- a/core-principles/rules-for-extending.md
+++ b/core-principles/rules-for-extending.md
@@ -10,7 +10,7 @@ In particular any change to an API design MUST follow the following Rules for Ex
 4. **Anything you add MUST be optional** (related [Robustness Principle](core-principles/robustness.md))
 
 
-> These rules covers also renaming and changes to identifiers (URIs). Names and identifiers should be stable over the time including their semantics.
+> NOTE: These rules covers also renaming and changes to identifiers (URIs). Names and identifiers should be stable over the time including their semantics.