At present, tx.fhir.org and other conformant terminology services (e.g. Ontoserver) return a parameter in ValueSet.expansion.parameter called 'version' which is the version (or not) of a resource that was used generating the expansion. 

This parameter is not documented anywhere, and 'version' is the wrong name (it's got that name for historical reasons, as the purpose behind it morphed). It's the parameter that leads to "based on LOINC 2.74" on the Value set expansions, which is important.

This task proposes to split the parameter into 3 different parameters, and document them (see also task 41589):

• used-system : uri. The canonical URL (system | {version} if available) of a code system that was used during the expansion of the value set 
• used-supplement: uri. The canonical URL (system | {version} if available) of a code system supplement that was used during the expansion of the value set 
• used-valueset: urii. The canonical URL (system | {version} if available) of a different value set that was used during the expansion of the value set 

Note that the type us uri not canonical since the parameter types is limited to uri, canonical is a sub-type of uri, and we will preadopt this parameter immediately. 

Further, we should add a description of these parameters as part of a new section "ValueSet Expansion Parameters" on the Value Set page, where also added the content added as a result of FHIR-41589