Address review comment

See #842 (comment)

index.bs

@@ -1836,9 +1836,20 @@ attributes.
     };
 </xmp>
 
-This enumeration is used to describe the [=attachment modality=] of an [=authenticator=] used to create a [=public key
-credential|credential=] - either by the [=[RP]=] to express a preferred [=attachment modality=], or by the [=client=] to report
-the [=attachment modality=] of an [=authenticator=] that was used.
+This enumeration's values describe [=authenticators=]' [=attachment modalities=]. [=[RPS]=] use this for two purposes:
+
+- to express a preferred [=authenticator=] [=attachment modality=] when calling
+    {{CredentialsContainer/create()|navigator.credentials.create()}} to [[#createCredential|create a credential]], and
+
+- to inform the [=client=] of the [=[RP]=]'s best belief about how to locate the [=managing authenticators=] of the
+    [=credentials=] listed in {{PublicKeyCredentialRequestOptions/allowCredentials}} when calling
+    {{CredentialsContainer/get()|navigator.credentials.get()}}.
+
+<!-- The following text would be added by PR #882 https://github.com/w3c/webauthn/pull/882
+
+[=Clients=] use it to report an employed [=authenticator=]'s [=attachment modality=] after [[#createCredential|creating a
+credential]] as a result of the [=[RP]=] calling {{CredentialsContainer/create()|navigator.credentials.create()}}.
+-->
 
 <div dfn-type="enum-value" dfn-for="AuthenticatorAttachment">
     :   <dfn>platform</dfn>