Clarify that the platform authenticator must be local.

Since hybrid allows remote platform authenticators to be used, the
previous wording was potentially ambiguous.

index.bs

@@ -3957,7 +3957,7 @@ Note: The {{PublicKeyCredentialHints}} enumeration is deliberately not reference
     ::  Indicates that the [=[RP]=] believes that users will satisfy this request with a physical security key. For example, an enterprise [=[RP]=] may set this hint if they have issued security keys to their employees and will only accept those [=authenticators=] for [=registration ceremony|registration=] and [=authentication ceremony|authentication=]. For compatibility with older user agents, when this hint is used in {{PublicKeyCredentialCreationOptions}}, the {{AuthenticatorSelectionCriteria/authenticatorAttachment}} SHOULD be set to {{AuthenticatorAttachment/cross-platform}}.
 
     :   <dfn>local-device</dfn>
-    ::  Indicates that the [=[RP]=] believes that users will satisfy this request with a [=platform authenticator=]. For compatibility with older user agents, when this hint is used in {{PublicKeyCredentialCreationOptions}}, the {{AuthenticatorSelectionCriteria/authenticatorAttachment}} SHOULD be set to {{AuthenticatorAttachment/platform}}.
+    ::  Indicates that the [=[RP]=] believes that users will satisfy this request with a [=platform authenticator=] attached to the local device. For compatibility with older user agents, when this hint is used in {{PublicKeyCredentialCreationOptions}}, the {{AuthenticatorSelectionCriteria/authenticatorAttachment}} SHOULD be set to {{AuthenticatorAttachment/platform}}.
 
     :   <dfn>hybrid</dfn>
     ::  Indicates that the [=[RP]=] believes that users will satisfy this request with general-purpose [=authenticators=] such as smartphones. For example, a consumer [=[RP]=] may believe that only a small fraction of their customers possesses dedicated security keys. This option also implies that the local [=platform authenticator=] should not be promoted in the UI. For compatibility with older user agents, when this hint is used in {{PublicKeyCredentialCreationOptions}}, the {{AuthenticatorSelectionCriteria/authenticatorAttachment}} SHOULD be set to {{AuthenticatorAttachment/cross-platform}}.