Index: include/clang/Basic/DiagnosticGroups.td
===================================================================
--- include/clang/Basic/DiagnosticGroups.td	(revision 150458)
+++ include/clang/Basic/DiagnosticGroups.td	(working copy)
@@ -332,7 +332,9 @@
 // Thread Safety warnings 
 def ThreadSafety : DiagGroup<"thread-safety">;
 
-// -Wall is -Wmost -Wparentheses -Wdangling-else -Wswitch
+// Note that putting warnings in -Wall will not disable them by default. If a
+// warning should be active _only_ when -Wall is passed in, mark it as
+// DefaultIgnore in addition to putting it here.
 def : DiagGroup<"all", [Most, Parentheses, Switch]>;
 
 // Aliases.