title: How to open a popup window in web forms without ajax modelpopupextender
body: <p>I am a windows forms developer and learning asp.net. I want to open a form as show dialog, means if I click the button another form has to popup and user should not able to click the backgroung page(like alert or confirm but has to contain controls). It is possible with ajax popupextender control. I tried like </p>
  
  <pre><code>(Javascript)  function OpenPopup(ctrlid) {                  
                window.open("testControls.aspx?ctrlid=" + ctrlid,"List","left = 300, top=150,scrollbars=no,resizable=no,width=400,height=280");
                return false;
            }
  </code></pre>
  
  <p>and code behind</p>
  
  <pre><code>Button1.Attributes.Add("onclick", "javascript:return OpenPopup('" + this.txtlevel2.ClientID + "')");
  </code></pre>
  
  <p>It will open the another form but allows to click on behind page. Is there any posible to do this.</p>