Provides the repType.
Provides the repType. Can be a "def" or a primitive type.
optRepType and optRepTypeDef are different, because it is possible for the repType to be a primitive type. The resulting type would be difficult (maybe impossible?) to use as the type for an element, as a primitive repType would be missing any annotations that tell Daffodil what the physical characteristics are; however the type can be used purely to define a function for use by DPath expressions.
optRepTypeDef - there is no "def" for a primitive type.