Currently ActivityDefinition.topic has an example [DefinitionTopic ValueSet|http://build.fhir.org/valueset-definition-topic.html], which consists of three values: treatment, education, assessment. 

This example DefinitionTopic valueset is abstract and describes the high level function of a PlanDefinition or ActivityDefinition. 

Drilling down a level, an ActivityDefinition's topic could also be used to describe the intent or content of the activity. For example, an ActivityDefinition.topic could define the type of activity, e.g.: diabetes-screening, zika-screening, mammography-screening, colonoscopy-screening, fecal-occult-blood-screening, or perhaps even pama-auc-evaluation.

For example, a PlanDefinition.topic of treatment and an ActivityDefinition.topic of zika-screening are complementary.

It would be nice to provide an additional example codesystem within this DefinitionTopic valueset with these slightly lower level values. 

I'm specifically interested in getting this created to harmonize with the proposed CDS Hooks' card.source.topic.