Leading or trailing blanks on String values (often called whitespace) might cause imprecise matching to the output from rules. While the default behavior of trimming whitespaces is often preferred, you can add com.corticon.tester.trimstringvalues=false to your brms.properties file to tell Corticon Studio to not perform trimming, and thus reduce validation mismatches. The default behavior is apparent when copying the output to the Expected column, as that action strips whitespaces, and often reveals apparent mismatches immediately.