representations: remove redundant normative language (normative reqs …

…are more explicit in subsequent sentences) towards #384

index.html

@@ -2283,7 +2283,7 @@ <h2>Service Endpoints</h2>
     <h1>Core Representations</h1>
 
     <p>
-All concrete representations of a <a>DID document</a> MUST be serialized using a
+All concrete representations of a <a>DID document</a> are serialized using a
 deterministic mapping that is able to be unambiguously parsed into the data
 model defined in this specification. All serialization methods MUST define rules
 for the bidirectional translation of a <a>DID document</a> both into and out of