The current QDM to QICore mapping maps "Encounter, Performed.code" to Encounter.class. For quality measure calculation, many of the Encounter value sets use CPT as the underlying code system, and thus should be represented in an attibute that supports this system. My perspective is that Encounter.type makes more sense based on the current attribute definitions in QI-Core v3. The primary reasons are that Encounter.class has a preferred binding to ActEncounterCodes and only supports a cardinality of 0..1. The Encounter.type attribute is defined more flexibly to allow implementers to codify encounters as required by the use case (in this case, the quality value sets). If an encounter includes multiple CPT codes, this can be supported in Encounter.type where the cardinality is 0..*.

See this Zulip thread for more information - Representing CPT codes for Encounters