Loading a UserControl within another UserControl code

I got the following code from the MDSN on line libray:

<%@ Page Language="C#" %>
<%@ Reference Control="~/Controls/Spinner.ascx" %>
<script runat="server">
private ASP.Spinner Spinner1
protected void Page_Load(object sender, EventArgs e)
{
  Spinner1 = (ASP.Spinner)LoadControl("~/Controls/Spinner.ascx");
}
protected void Button1_Click(object sender, EventArgs e)
{
  PlaceHolder1.Controls.Add(Spinner1);
}
</script>

<asp:PlaceHolder runat="server" ID="PlaceHolder1" />
<br />
<asp:Button ID="Button1" runat="server" Text="Click to Add User Control" OnClick="Button1_Click" />

basically you have to load the new control code behind and attach it in a place older so you have to set a PlaceHolder in the first control or something that can contains the Child-Control

This is the MSDN ref: http://msdn.microsoft.com/en-us/library/c0az2h86(v=vs.100).aspx