Update custom_controls.adoc

src/docs/asciidoc/jme3/advanced/custom_controls.adoc

@@ -152,3 +152,37 @@ public class MyControl extends AbstractControl implements Savable, Cloneable {
     }  
 }
 ----
+
+See also:
+
+*  To learn more about `write()` and `read()`, see <<jme3/advanced/save_and_load#,Save and Load>>
+*  To learn more about `setUserData()`, see <<jme3/advanced/spatial#,Spatial>>.
+
+
+== The Control Interface
+
+
+[TIP]
+====
+In the less common case that you want to create a Control that also extends another class, create a custom interface that  extends jME3's Control interface. Your class can become a Control by implementing the Control interface, and at the same time extending another class.
+====
+
+
+The Control interface can be found under `com.jme3.scene.control.Control`. It has the following method signatures:
+
+*  `cloneForSpatial(Spatial)`: Clones the Control and attaches it to a clone of the given Spatial. +
+Implement this method to be able to <<jme3/advanced/save_and_load#,save() and load()>> Spatials carrying this Control. +
+The AssetManager also uses this method if the same spatial is loaded twice. You can specify which fields you want your object to reuse (e.g. collisionshapes) in this case. 
+*  `setEnabled(boolean)`: Toggles a boolean that enables or disables the Control. Goes with accessor `isEnabled();`. You test for it in the `update(float tpf)` loop before you execute anything.
+*  There are also some internal methods that you do not call from user code: `setSpatial(Spatial s)`, `update(float tpf);`, `render(RenderManager rm, ViewPort vp)`.
+
+Usage example:
+
+. Create a custom control interface.
++
+[source,java]
+----
+public interface MyControlInterface extends Control {    
+    public void setSomething(int x); // optionally, add custom methods
+}
+----