diff --git a/include/boost/core/noncopyable.hpp b/include/boost/core/noncopyable.hpp
index ab30505..4a4f8ba 100644
--- a/include/boost/core/noncopyable.hpp
+++ b/include/boost/core/noncopyable.hpp
@@ -23,6 +23,14 @@ namespace noncopyable_  // protection from unintended ADL
 #ifndef BOOST_NONCOPYABLE_BASE_TOKEN_DEFINED
 #define BOOST_NONCOPYABLE_BASE_TOKEN_DEFINED
 
+// noncopyable derives from base_token to enable Type Traits to detect
+// whether a type derives from noncopyable without needing the definition
+// of noncopyable itself.
+//
+// The definition of base_token is macro-guarded so that Type Trais can
+// define it locally without including this header, to avoid a dependency
+// on Core.
+
   struct base_token {};
 
 #endif // #ifndef BOOST_NONCOPYABLE_BASE_TOKEN_DEFINED