From Atlas to ASP.NET AJAX: Client Controls

I have always had my beef with the client controls Atlas introduced. I am using JavaScript since approximately ten years now, so I know my way around DOM fairly well. So why add another layer in between? Of course there are scenarios where that makes sense, and there are developers who really appreciate a rather consistent API.
When upgrading to ASP.NET AJAX, client controls are gone at first. You need to install the CTP first. Then, some details change. First of all, the namespace moved from Sys.UI to Sys.Preview.UI. However in order to be able to access Sys.Preview.UI, an additional library must be loaded via the ScriptManager:

<asp:ScriptManager ID="ScriptManager1" runat="server">
  <Scripts>
    <asp:ScriptReference
      Name="Microsoft.Web.Resources.ScriptLibrary.PreviewScript.js"
      Assembly="Microsoft.Web.Preview" />
  </Scripts>
</asp:ScriptManager>

Apart from that, not very much changes. One notable exception: Sys.UI.Select is gone; it is now called Sys.Preview.UI.Selector. I wonder why, but it works

(Part of the Atlas to ASP.NET AJAX Migration series.)