Adding new popup window (modal) to a webpage

Adding new popup window (modal) to a webpage is not that hard, but can be a little tricky.

let's describe how it should be done :

1. We create an asp:Panel 
   
2. We create an modalPopupExtender. It is located in the AjaxControlToolkit 
   
3. We Create a Hidden Button . Something has to be a trigger for a popup to show up. If you do that as I do , meaning you make a modal to show up on screen using a Javascript (latter) you still have to create a control to trigger the modal. That's why we create a asp:button.
   
   <asp:button id="openModal1" runat="server">
   
    
   
4. Configuration 
5. 1-ModalPopupExtender :  
   TargetControlID should point to the button or the control we want to trigger the popup
   
   PopupControlID should point to the panel we want to open (step 2 )
   
   BehaviorID is the clientside name of the popup .. if we want to call it from  the HTML\javascript $find('behID').show(); will show up the popup . 
   2-Panel the Id has to the the value in the PopupControlID
6. Then, we add the script that shows up the modal , something like :
   function onLoad(){
   $find('behID').show();
   }
7. note that the value in the brackets points to the behaviorID proterty of the ModalPopupExtender