A field check. Return a ValidationResult, or true/null to pass, false to fail with a default message, or a string to fail with that message. A successful ValidationResult replaces the field value in the parsed output.
ValidationResult
true
null
false
Optional
A field check. Return a
ValidationResult, ortrue/nullto pass,falseto fail with a default message, or a string to fail with that message. A successfulValidationResultreplaces the field value in the parsed output.