Use case
Return "Valid" if the custom field value matches the regular expression and "Invalid" if it does not.
Expression
Create and configure a Smart field using this expression in General parsing mode:
%{matches(%{issue.cfnnnnn},"6|7|8|9") ? "Valid":"Invalid"}
The values entered as arguments in the matches() parser function can be replaced with different values or with a regular expressions to validate differently the value of the custom field.
Please, note that it is necessary to replace nnnnn with the ID of the custom field.
