How and when does FileMaker Pro decide when to check validation? FileMaker Pro runs valdiations at the time a record is committed. Committing is the term for FileMaker Pro's automatic saving process, which can happen in a number of ways. Clicking on whitespace and switching to another record are the most common ways users commit a record. If all field validations pass, the record is silently saved. If a validation fails, the record is not saved and the user sees a message like the one in figure 2. Unique Value and Existing Value validations are exceptions; they validate as soon as you exit the field.
But if validation happens on commit, what's the difference between validating "Always" versus "Only during data entry, as shown in figure 1? Choosing "Always" means FileMaker Pro performs field validation each time a user views a record. "Only during data entry" only validates if the user makes a change to the record.
The message in figure 2 is notoriously confusing to users. Clicking on Yes means "I know this field value breaks the rules, but I'm going to keep it anyway." Clicking on No means "I didn't mean to break the rule and I'd like to go back and fix it." Clicking on the Revert Record option means "Forget it. Change this whole record back to the way it was before I started making changes." It also means "Throw the baby out with the bath water." The Revert Record option tosses out any change to any field in the current record that was entered after the last time it was committed.
-- Stuart