title: Is it possible to directly reference doxygen built-in modules in the layout file?
body: <p>I am trying to customize doxygen output using the layout file.</p>
  
  <pre><code>&lt;tab type="modules" visible="yes" title="" intro=""&gt;
      &lt;tab type="user" visible="yes" title="High-level document interface" url="@ref Documents"/&gt;
      &lt;tab type="user" visible="yes" title="Low-level file interface" url="@ref Files"/&gt;
      &lt;tab type="user" visible="yes" title="Utilities" url="@ref Utils"/&gt;
      &lt;tab type="user" visible="yes" title="Types" url="@ref Types"/&gt;
  &lt;/tab&gt;
  </code></pre>
  
  <p>The output has one minor problem, that the user defined pages are duplicated in the tree view.</p>
  
  <p><a href="https://i.stack.imgur.com/Xrhss.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Xrhss.png" alt="enter image description here"></a></p>
  
  <p>I have tried using custom user group and referencing the modules from the layout file as following:</p>
  
  <pre><code>&lt;tab type="usergroup" visible="yes" url="@ref modules" title="Modules"&gt;
  </code></pre>
  
  <p>However I end up with error: "<strong>explicit link request to 'modules' in layout file 'doxygen_layout.xml' could not be resolved</strong>"</p>
  
  <p>This can be solved referencing the modules.html file.</p>
  
  <pre><code>&lt;tab type="usergroup" visible="yes" url="modules.html" title="Modules"&gt;
  </code></pre>
  
  <p>I was really surprised this works, but I am not sure if it is the most bullet-proof solution.</p>
  
  <p><strong>Can I create drop-down modules menu?</strong></p>
  
  <p><strong>Can I directly reference to modules page?</strong></p>
  
  <p>Note:
  Referencing non-existing html file does not produce any warning nor error in the output.</p>
  
  <pre><code>&lt;tab type="usergroup" visible="yes" url="asdf.html" title="Modules"&gt;
  </code></pre>