define platform passkey authenticator

index.bs

@@ -4296,8 +4296,8 @@ For example:
 
 The above examples illustrate the primary <dfn>authenticator type</dfn> characteristics:
 
-- Whether the [=authenticator=] is a [=roaming authenticator|roaming=] or [=platform authenticator|platform=] authenticator
-    &mdash; the [=authenticator attachment modality=].
+- Whether the [=authenticator=] is a [=roaming authenticator|roaming=] or [=platform authenticator|platform=] authenticator,
+    or in some cases both &mdash; the [=authenticator attachment modality=].
     A [=roaming authenticator=] can support one or more [[#enum-transport|transports]] for communicating with the [=client=].
 - Whether the authenticator is capable of [=user verification=] &mdash; the [=authentication factor capability=].
 - Whether the authenticator is [=discoverable credential capable=] &mdash; the [=credential storage modality=].
@@ -4342,6 +4342,12 @@ lists and names some [=authenticator types=] of particular interest.
                 <td> [=client-side credential storage modality|Client-side storage=] </td>
                 <td> [=Multi-factor capable=] </td>
             </tr>
+            <tr>
+                <th> <dfn>Platform passkey authenticator</dfn> </th>
+                <td> [=platform attachment|platform=] ({{AuthenticatorTransport|transport}} = {{AuthenticatorTransport/internal}}) or [=cross-platform attachment|cross-platform=] ({{AuthenticatorTransport|transport}} = {{AuthenticatorTransport/hybrid}})</td>
+                <td> [=client-side credential storage modality|Client-side storage=] </td>
+                <td> [=Multi-factor capable=] </td>
+            </tr>
         </tbody>
     </table>
     <figcaption>