SL_3 'Do not add non-standard entities to namespace `std`' add example
diff --git a/CppCoreGuidelines.md b/CppCoreGuidelines.md
index c418cc12e..e3e391c19 100644
--- a/CppCoreGuidelines.md
+++ b/CppCoreGuidelines.md
@@ -19757,7 +19757,17 @@ Additions to `std` might clash with future versions of the standard.
 
 ##### Example
 
-    ???
+    namespace std { // BAD: violates standard
+        class My_vector {
+        //     . . .
+        };
+    }
+
+    namespace Foo { // GOOD: user namespace is allowed 
+        class My_vector {
+        //     . . .
+        };
+    }
 
 ##### Enforcement
 
diff --git a/scripts/hunspell/isocpp.dic b/scripts/hunspell/isocpp.dic
index beaa83b8e..0b5575346 100644
--- a/scripts/hunspell/isocpp.dic
+++ b/scripts/hunspell/isocpp.dic
@@ -346,6 +346,7 @@ Murray93
 mutex
 mutexes
 mx
+My_vector
 MyCustomError
 MyException
 myMap

Add simple example