ASP.NET Call Parent ModalPopupExtender (javascript or jquery)

I have an aspx page with an iFrame. The iFrame's src is set to a child aspx page.

I somehow need to display a modal popup form on the parent aspx page, to be shown when clicking a button on the child aspx page.

Something like:

Function ShowIt()
  {
   document.parent.getElemtentById("<%= modal.clientID %>").show();

          // Or

   $parent.find('modal').show();
  }

Any ideas would be greatly appreciated!

Thanks,

Jason

Set BehaviorID property value for a ModalPopupExtender and use this script : window.parent.$find('behaviorId').show();