diff --git a/lldb/source/Commands/CommandObjectExpression.cpp b/lldb/source/Commands/CommandObjectExpression.cpp
index ee05360..a93d4e6 100644
--- a/lldb/source/Commands/CommandObjectExpression.cpp
+++ b/lldb/source/Commands/CommandObjectExpression.cpp
@@ -164,7 +164,7 @@
 CommandObjectExpression::CommandObjectExpression (CommandInterpreter &interpreter) :
     CommandObjectRaw (interpreter,
                       "expression",
-                      "Evaluate a C/ObjC/C++ expression in the current program context, using variables currently in scope.",
+                      "Evaluate a C/ObjC/C++ expression in the current program context, using user defined variables and variables currently in scope.",
                       NULL,
                       eFlagProcessMustBePaused),
     m_option_group (interpreter),
@@ -180,10 +180,18 @@
     currently .25 seconds.  If it doesn't return in that time, the evaluation will be interrupted\n\
     and resumed with all threads running.  You can use the -a option to disable retrying on all\n\
     threads.  You can use the -t option to set a shorter timeout.\n\
+\n\
+User defined variables:\n\
+    You can define your own variables for convenience or to be used in subsequent expressions.\n\
+    You define them the same way you would define variables in C.  If the first character of \n\
+    your user defined variable is a $, then the variable's value will be available in future\n\
+    expressions, otherwise it will just be available in the current expression.\n\
+\n\
 Examples: \n\
 \n\
    expr my_struct->a = my_array[3] \n\
    expr -f bin -- (index * 8) + 5 \n\
+   expr unsigned int $foo = 5\n\
    expr char c[] = \"foo\"; c[0]\n");
 
     CommandArgumentEntry arg;