DDR Simple API - Section 4.2.1 Evidence Interface : clarification needed

+ Section 4.2.1 Evidence Interface

Is the Evidence interface a generic interface or an specific interface for representing Evidence in the form of HTTP headers?
If it is a generic interface, as I see it, then 4.2.1.1 1. Add Evidence should be repharased to:

 AddEvidence(key,value)
Query Evidence (key)
Retrieve Evidence (key)