minor doc update

docs/graph2d.html

@@ -247,7 +247,7 @@ groups.add({
         <td>visible</td>
         <td>Boolean</td>
         <td>true</td>
-        <td>This field is optional. If false, the graph will not be drawn.
+        <td>This field is optional. If false, this group will not be drawn.
     </tr>
 </table>