Why are all “SuperType” properties defined as attributes?

The “SuperType” contains properties that are applicable to all components of the GJXDM; therefore, all fields will include the properties of “SuperType”. All GJXDM components are derived from “SuperType”, so that all components inherit all the “SuperType” properties. At the same time, “SuperType” has neither complex nor simple content. In fact, it has no content; it's empty. Thus, objects with simple content can still be derived from “SuperType”, because it cannot contain any subordinate elements. And finally, one can consider “SuperType” properties generic enough to be metadata (such as, “probabilityNumeric”, “distributionText”, “reportedDate”, “expirationDate”, etc.) on all GJXDM components.