add another example + notes on event management

Chapters/bloc/events.md

@@ -1,14 +1,7 @@
 ## Event handling
 
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 ### Event handling
 
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 ```smalltalk
 BlElement new 
   background: Color white; 
@@ -20,6 +13,9 @@ BlElement new
 ```
 
 `addEventHandlerOn:do:` returns the new handler so that we can store to remove it in case. 
+
+#addEventHandlerOn: do: returns the new event handler.  add a #yourself send after to return a BlElement.
+
 `when:do:` is now deprecated and rewritten as `addEventHandlerOn:do:`
 SD: we should update the following
 
@@ -38,13 +34,29 @@ We should check `example_mouseEvent_descending_bubbling`
 
 ![Windows nested in each others in Toplo.](figures/4windows.png width=80)
 
+To stop event propagation `anEvent consumed: true`
 
+There is an option to forbid mouse events for an element. 
+You just send `preventMouseEvent` to it
 
+```smalltalk
+"As a more general explanation, all UI related events can be controlled. Have a look at BlElementFlags and BlElementEventDispatcherActivatedEvents and how these classes are used. "
+
+container := BlElement new size: 500 asPoint; border: (BlBorder paint: Color red width: 2).
 
 
+"#addEventHandlerOn: do: returns the new event handler.  add a #yourself send after"
+child1 := BlElement new size: 300 asPoint; background: Color lightGreen; position: 100 asPoint; addEventHandlerOn: BlClickEvent do: [ self inform: '1' ]; yourself .
 
+"There is an option to forbid mouse events for an element. 
+You just send #preventMouseEvent to it."
+child2 := BlElement new size: 200 asPoint; position: 200 asPoint; border: (BlBorder paint: Color blue width: 2);preventMouseEvents.
 
+container addChild: child1.
+container addChild: child2.
 
+container openInSpace.
+```
 
 ### Drag&drop