Handling Validation Errors
When a validation rule throws exceptions, the exceptions are bundled and returned to the client, and any database changes pertaining to the transaction are rolled back.
The Failure Handling tab in the Validation page of the Validation Rule page of the entity object editor (or the attribute editor) is where you specify the error message that you want to display to the end user when the validation fails.
You use the Validation Failure Severity option buttons to specify whether the message is an Error message (default) or Informational Warning.
You can enter Groovy expressions to populate variables in error message text to make the message more meaningful. And you can store messages in a resource bundle or property file to make them translatable.