Clarify behaviour of duplicate hints

index.bs

@@ -4473,6 +4473,7 @@ Note: The {{PublicKeyCredentialHints}} enumeration is deliberately not reference
 
 <div dfn-type="enum-value" dfn-for="PublicKeyCredentialHints">
     [=[WRPS]=] may use this enumeration to communicate hints to the user-agent about how a request may be best completed. These hints are not requirements, and do not bind the user-agent, but may guide it in providing the best experience by using contextual information that the [=[RP]=] has about the request. Hints are provided in order of decreasing preference so, if two hints are contradictory, the first one controls. Hints may also overlap: if a more-specific hint is defined a [=[RP]=] may still wish to send less specific ones for user-agents that may not recognise the more specific one. In this case the most specific hint should be sent before the less-specific ones.
+    If the same hint appears more than once, its second and later appearences are ignored.
 
     Hints MAY contradict information contained in credential {{PublicKeyCredentialDescriptor/transports}} and {{AuthenticatorSelectionCriteria/authenticatorAttachment}}. When this occurs, the hints take precedence. (Note that {{PublicKeyCredentialDescriptor/transports}} values are not provided when using [=discoverable credentials=], leaving hints as the only avenue for expressing some aspects of such a request.)