KERML_ — Some types not given any semantics

The Type metaclass is concrete (like all the metaclasses in the abstract syntax), making it it syntactically valid to create a Type that is not a Classifier or a Feature. However, Clause 8.4.3.1.2 (Core Semantics Mathematical Preliminaries) requires the set of Types in a model to be the union of the set of Classifiers and Features. This means instances of Type in a model that are not Classifiers or Features are syntactically valid, but not given semantics (it's not possible to tell if instances of such types are valid or not).