Clarify semantics of isPlatformAuthenticatorAvailable

This closes #627.

index.bs

@@ -1189,9 +1189,9 @@ When this method is invoked, the user agent MUST execute the following algorithm
 
 <div link-for-hint="WebAuthentication/isPlatformAuthenticatorAvailable">
 
-[=[RPS]=] use this method to determine whether they can create a new credential using a [=platform authenticator=].
-Upon invocation, the [=client=] employs a platform-specific procedure to discover available [=platform authenticators=].
-If successful, the [=client=] then assesses whether the user is willing to create a credential using one of the available [=platform authenticators=].
+[=[RPS]=] use this method to determine whether they can create a new credential using a user verifying [=platform authenticator=].
+Upon invocation, the [=client=] employs a platform-specific procedure to discover available user-verifying [=platform authenticators=].
+If successful, the [=client=] then assesses whether the user is willing to create a credential using one of the available user verifying [=platform authenticators=].
 This assessment may include various factors, such as:
     - Whether the user is running in private or incognito mode.
     - Whether the user has configured the [=client=] to not create such credentials.
@@ -3799,7 +3799,7 @@ The sample code for generating and registering a new key follows:
 ## Registration Specifically with Platform Authenticator ## {#sample-registration-with-platform-authenticator}
 
 This is flow for when the [=[RP]=] is specifically interested in creating a public key credential with
-a [=platform authenticator=].
+a user verifying [=platform authenticator=].
 
 1. The user visits example.com and clicks on the login button, which redirects the user to login.example.com.