Updated FAQ (markdown)

FAQ.md

@@ -277,7 +277,33 @@ void sendJson(JsonVariant json) {
 }
 ```
 
-See issue [#195](https://github.com/bblanchon/ArduinoJson/issues/195)
+But in that case, you loose some specificities of the `JsonObject` class.
+In particular, you don't have the `containsKey()` method.
+If you need this function, you must cast the `JsonVariant` back to a `JsonObject&`.
+
+For instance:
+
+```c++
+void myFunction(JsonVariant variant)
+{
+    if (variant.is<JsonArray&>())
+    {
+        JsonArray& array = variant;
+        // ...
+    }
+    else if (variant.is<JsonObject&>()) 
+    {
+        JsonObject& object = variant;
+        // ...
+    }
+    else
+    {
+        // ...
+    }
+}
+```
+
+See issue [#195](https://github.com/bblanchon/ArduinoJson/issues/195) and [#196](https://github.com/bblanchon/ArduinoJson/issues/196)
 
 ### What are the differences between `StaticJsonBuffer` and `DynamicJsonBuffer`?