Annotation used to mark a method as being suitable for converting an
object to a standard format
String.
This annotation should be applied to one method on a class.
The method must not be static. It must take no parameters and return a String.
The string format must be able to be parsed by the matching @FromString on
the same class. The format should be human readable and an industry standard
where possible, for example ISO-8601 for dates and times.