diff --git a/cs3/gateway/v1beta1/gateway_api.proto b/cs3/gateway/v1beta1/gateway_api.proto
index 8d4c4cf6..18aacf23 100644
--- a/cs3/gateway/v1beta1/gateway_api.proto
+++ b/cs3/gateway/v1beta1/gateway_api.proto
@@ -537,8 +537,14 @@ message OpenInAppRequest {
     VIEW_MODE_VIEW_ONLY = 1;
     // The resource can be downloaded.
     VIEW_MODE_READ_ONLY = 2;
-    // The resource can be downloaded and updated.
+    // The resource can be downloaded and updated. The underlying application
+    // MUST be a fully capable editor to support this mode.
     VIEW_MODE_READ_WRITE = 3;
+    // The resource can be downloaded and updated, but must be shown in
+    // preview mode. If the underlying application does not support a preview mode,
+    // or if in a view-only mode users are not allowed to switch to edit mode,
+    // then this mode MUST fall back to READ_WRITE.
+    VIEW_MODE_PREVIEW = 4;
   }
   ViewMode view_mode = 3;
   // OPTIONAL.
diff --git a/docs/index.html b/docs/index.html
index 6d03f736..17f61aa1 100644
--- a/docs/index.html
+++ b/docs/index.html
@@ -2474,7 +2474,17 @@ <h3 id="cs3.gateway.v1beta1.OpenInAppRequest.ViewMode">OpenInAppRequest.ViewMode
               <tr>
                 <td>VIEW_MODE_READ_WRITE</td>
                 <td>3</td>
-                <td><p>The resource can be downloaded and updated.</p></td>
+                <td><p>The resource can be downloaded and updated. The underlying application
+MUST be a fully capable editor to support this mode.</p></td>
+              </tr>
+            
+              <tr>
+                <td>VIEW_MODE_PREVIEW</td>
+                <td>4</td>
+                <td><p>The resource can be downloaded and updated, but must be shown in
+preview mode. If the underlying application does not support a preview mode,
+or if in a view-only mode users are not allowed to switch to edit mode,
+then this mode MUST fall back to READ_WRITE.</p></td>
               </tr>
             
           </tbody>