Provide a reference for RP implementors as to what errors might be av…

…ailable during WebAuthn create/get ceremonies

index.bs

@@ -4360,7 +4360,10 @@ In order to perform a [=registration ceremony=], the [=[RP]=] MUST proceed as fo
 1. Call {{CredentialsContainer/create()|navigator.credentials.create()}} and pass |options|
     as the <code>{{CredentialCreationOptions/publicKey}}</code> option.
     Let |credential| be the result of the successfully resolved promise.
-    If the promise is rejected, abort the ceremony with a user-visible error.
+    If the promise is rejected, abort the ceremony with a user-visible error, or otherwise guide the user experience as
+    might be determinable from the context available in the rejected promise. For example if the promise is rejected with
+    an error code equivalent to "{{InvalidStateError}}", the user might be instructed to use a different [=authenticator=]. 
+    For information on different error contexts and the circumstances leading to them, see [=authenticatorMakeCredential=].
 
 1. Let |response| be <code>|credential|.{{PublicKeyCredential/response}}</code>.
     If |response| is not an instance of {{AuthenticatorAttestationResponse}}, abort the ceremony with a user-visible error.
@@ -4497,7 +4500,9 @@ In order to perform an [=authentication ceremony=], the [=[RP]=] MUST proceed as
 1. Call {{CredentialsContainer/get()|navigator.credentials.get()}} and pass |options|
     as the <code>{{CredentialRequestOptions/publicKey}}</code> option.
     Let |credential| be the result of the successfully resolved promise.
-    If the promise is rejected, abort the ceremony with a user-visible error.
+    If the promise is rejected, abort the ceremony with a user-visible error, or otherwise guide the user experience as might 
+    be determinable from the context available in the rejected promise. For information on different error contexts and the 
+    circumstances leading to them, see [=authenticatorGetAssertion=].
 
 1. Let |response| be <code>|credential|.{{PublicKeyCredential/response}}</code>.
     If |response| is not an instance of {{AuthenticatorAssertionResponse}}, abort the ceremony with a user-visible error.