Fix #2163: improve comments for addProcess() and the preamble.
diff --git a/StandAlone/StandAlone.cpp b/StandAlone/StandAlone.cpp
index c3ae2b4..88b305c 100644
--- a/StandAlone/StandAlone.cpp
+++ b/StandAlone/StandAlone.cpp
@@ -242,6 +242,7 @@
     std::string text;  // contents of preamble
 };
 
+// Track the user's #define and #undef from the command line.
 TPreamble UserPreamble;
 
 //