A StringReaderProvider is responsible for providing an instance of this interface.

If annotated with StringReader.ValidateDefaultValue with a value of true or the annotation is absent then the reader will be used to validate a default value (if any) by calling the fromString method, perhaps at initialization, before any value, default or otherwise, is actually required. This enables the early reporting of errors for default values. If annotated with StringReader.ValidateDefaultValue with a value of false then the reader will not be used to validate a default (if any) before any value, default or otherwise, is actually required.