title: Content controls have to be top-level controls in a content page or a nested master page that references a master page
body: <p>I want to use nested master page so i create the following master page :</p>
  
  <pre><code>&lt;%@ Master Language="C#" AutoEventWireup="true" CodeBehind="test.master.cs" Inherits="DocumentFlowUI.test" MasterPageFile="~/MasterPage2.master" %&gt;
  
  &lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"&gt;
  &lt;html xmlns="http://www.w3.org/1999/xhtml"&gt;
  &lt;head runat="server"&gt;
      &lt;title&gt;&lt;/title&gt;
      &lt;asp:ContentPlaceHolder ID="head" runat="server"&gt;
      &lt;/asp:ContentPlaceHolder&gt;
  &lt;/head&gt;
  &lt;body&gt;
      &lt;form id="form1" runat="server"&gt;
      &lt;div&gt;
          &lt;asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server"&gt;
              &lt;asp:Button ID="Button1" runat="server" Text="Button" /&gt;
          &lt;/asp:ContentPlaceHolder&gt;
      &lt;/div&gt;
      &lt;/form&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <hr>
  
  <p>and i create the following page to use that master page :</p>
  
  <pre><code>&lt;%@ Page Title="" Language="C#" MasterPageFile="~/test.Master" AutoEventWireup="true" CodeBehind="WebForm4.aspx.cs" Inherits="DocumentFlowUI.WebForm4" %&gt;
  &lt;asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server"&gt;
  &lt;/asp:Content&gt;
  &lt;asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server"&gt;
      &lt;asp:Label ID="Label1" runat="server" Text="Label"&gt;&lt;/asp:Label&gt;
  &lt;/asp:Content&gt;
  </code></pre>
  
  <hr>
  
  <p>I get the following error :</p>
  
  <blockquote>
    <p>Content controls have to be top-level controls in a content page or a
    nested master page that references a master page</p>
  </blockquote>