Doxygen tweaks

src/App/Expression.cpp

@@ -72,6 +72,11 @@
 #pragma warning(disable : 4065)
 #endif
 
+/** \defgroup Expression Expressions framework
+    \ingroup APP
+    \brief The expression system allows users to write expressions and formulas that produce values
+*/
+
 using namespace Base;
 using namespace App;