Index: include/clang/AST/Expr.h
===================================================================
--- include/clang/AST/Expr.h	(revision 170131)
+++ include/clang/AST/Expr.h	(working copy)
@@ -2306,6 +2306,9 @@
                             QualType ty, ExprValueKind VK, ExprObjectKind OK);
 
   void setBase(Expr *E) { Base = E; }
+
+  /// \brief Retrieve the base structure reference or pointer. For example,
+  /// for X.f, this would return X.
   Expr *getBase() const { return cast<Expr>(Base); }
 
   /// \brief Retrieve the member declaration to which this expression refers.