I followed the instructions you gave for creating a rule, but the rule didn't work!
NOTE: This article pertains to versions prior to 6.5.
In the example given for the @INSTR macro, the instructions do not mention that you should not have a space after @INSTR. To clarify:
Fails: @INSTR (IsNull)
Code Review does not check the syntax of macros in user defined rules. If the rule is not working, verify the syntax of any macros you used to define your rule.