--- a/src/core/uid-manager.h	Fri May 11 19:26:01 2007 +0200
+++ b/src/core/uid-manager.h	Fri May 11 22:33:51 2007 +0200
@@ -27,6 +27,9 @@
 
 namespace ns3 {
 
+/**
+ * zero is never a valid uid value.
+ */
 class UidManager
 {
 public: