CQL 1.5 introduced support for terminology types to allow references to terminology to be passed as arguments, rather than forcing an expand whenever a value set or code system is referenced. This capability is backwards-compatible, but there are cases where the translator is not accounting for the new capability correctly, resulting in errors when translating CQL that makes use of value set references as arguments to functions.

To improve backwards-compatibility, the following changes should be made to the specification:

1. Add a "name" element to the Vocabulary type to make the run-time representation of the terminology types more user-friendly.
2. Add a "codesystem" element to the ValueSet type to complete the representation of code system binding overrides used in value set declarations.
3. Add an "ExpandValueSet" function and ELM node to allow value set expansion to be represented explicitly in ELM.
4. Add a "preserve" attribute to the ValueSetRef node to allow engines to decide how to process value set references (i.e. expand, or return a ValueSet instance)
5. Add an implicit conversion in 1.5 from ValueSet to List<Code> using the ExpandValueSet operator

These changes have been implemented in the 1,5,6 translator (see 707(https://github.com/cqframework/clinical_quality_language/issues/707))