Range of datatype properties not explicitly defined

[renevoorburg]

RDA Registry claims: "Every RDA element has a datatype property with a range of Literal; every element can use a string value." (http://www.rdaregistry.info/rgGuide/). However, that range seems to be defined implicitly, not explicitly. For example, the definitions at http://www.rdaregistry.info/Elements/w/datatype/ don't seem to include any rdfs:range statements.

For clarity's sake, an explicite range definition would be preferred.