-C<A-Z, a-z, 0-9, -,_>, starting with a letter and a maximum length of 255 characters.
+C<A-Z, a-z, 0-9, -,_> and a maximum length of 255 characters.
+
+When picking variable names, make sure you do not choose a name that is
+already taken by an RPN operator. A save bet it to use lowercase or
+mixedcase names for variables since operators will always be in uppercase.