Feature summary (what you would like to be able to do and where):
Format constraint violation messages should show an example of a correct value.
Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
Regex Format constraints currently show only the regex.
Because regexes can be hard to interpret, it would be helpful to users like this one to show an example of the correct value so that they know how they can fix the value the inputted.
Benefits (why should this be implemented?):
Users can more-easily correct their constraint violations