Changed uses of JSON string to USVString (#739)

index.bs

@@ -3500,7 +3500,7 @@ JavaScript APIs.
 :: `appid`
 
 : Client extension input
-:: A single JSON string specifying a FIDO |AppID|.
+:: A single USVString specifying a FIDO |AppID|.
 
 : Client extension processing
 ::  1. If present in a {{CredentialsContainer/create()}} call, return a
@@ -3542,13 +3542,13 @@ This [=registration extension=] and [=authentication extension=] allows for a si
 :: `txAuthSimple`
 
 : Client extension input
-:: A single JSON string prompt.
+:: A single USVString prompt.
 
 : Client extension processing
 :: None, except creating the authenticator extension input from the client extension input.
 
 : Client extension output
-:: Returns the authenticator extension output string UTF-8 decoded into a JSON string
+:: Returns the authenticator extension output string UTF-8 decoded into a USVString
 
 : Authenticator extension input
 :: The client extension input encoded as a CBOR text string (major type 3).
@@ -3581,7 +3581,7 @@ as well. This allows authenticators without a font rendering engine to be used a
 :: None, except creating the authenticator extension input from the client extension input.
 
 : Client extension output
-:: Returns the base64url encoding of the authenticator extension output value as a JSON string
+:: Returns the base64url encoding of the authenticator extension output value as a USVString
 
 : Authenticator extension input
 :: The client extension input encoded as a CBOR map.
@@ -3680,7 +3680,7 @@ This [=registration extension=] and [=authentication extension=] enables use of
 :: None, except creating the authenticator extension input from the client extension input.
 
 : Client extension output
-:: Returns a JSON string containing the base64url encoding of the authenticator extension output
+:: Returns a USVString containing the base64url encoding of the authenticator extension output
 
 : Authenticator extension input
 :: The Boolean value `true`, encoded in CBOR (major type 7, value 21).