--- a/liboctave/lo-traits.h
+++ b/liboctave/lo-traits.h
@@ -23,6 +23,12 @@
 #if !defined (octave_liboctave_traits_h)
 #define octave_liboctave_traits_h 1
 
+// Ideas for these classes taken from C++ Templates, The Complete
+// Guide by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley
+// (2003).
+
+// Select a type based on the value of a constant expression.
+
 template <bool cond, typename T1, typename T2>
 class if_then_else;
 
@@ -42,6 +48,8 @@
   typedef T2 result;
 };
 
+// Determine whether a template paramter is a class type.
+
 template<typename T1>
 class is_class_type
 {
@@ -62,6 +70,9 @@
   enum { no = ! yes };
 };
 
+// Define typename ref_param<T>::type as T const& if T is a class
+// type.  Otherwise, define it to be T.
+
 template<typename T>
 class ref_param
 {