Clarify that a conforming document has two possible media types.

Author: msporny

index.html

@@ -3541,7 +3541,10 @@ <h3>Ecosystem Compatibility</h3>
 If conceptually aligned digital credential formats can be transformed into a
 <a>conforming document</a> according to the rules provided in this section, they
 are considered <em>"compatible with the Verifiable Credentials ecosystem"</em>.
-Specifications that are compatible with the Verifiable Credentials ecosystem:
+A <a>conforming document</a> is either a <a>verifiable credential</a> serialized
+as the `application/vc+ld+json` media type or a <a>verifiable presentation</a>
+serialized as the `application/vp+ld+json` media type. Specifications that are
+compatible with the Verifiable Credentials ecosystem:
         </p>
 
         <ul>