Implementation

Create a single navigation.xml that contains the menu structure for the entire document tree. Add all items and sub-items.

For items that can collapse when you are not browsing them, add collapse="true" to the item declaration. 

    	<?xml version="1.0" encoding="ISO-8859-1"?>
<project name="Maven xdoc Plugin">

  <title>Maven xdoc Plugin</title>

  <body>
    <links>
      <item name="Maven"  href="http://maven.apache.org/"/>
    </links>
    <menu>
      <item name="Alpha" href="/alpha/index.html">   
	      <item name="Alpha One" href="/alpha/one/index.html"/>
	      <item name="Alpha Two" href="/alpha/two/index.html"/>
	  </item>
      <item name="Beta" href="/beta/index.html" collapse="true">
	      <item name="Beta One" href="/beta/one/index.html" collapse="true"/>
	      <item name="Beta Two" href="/beta/two/index.html" collapse="true"/>
	  </item>
    </menu>
  </body>
</project>

Now the menus will expand and collapse as you navigate through them.

Caveats

  1. You must refer to subdirectories as /folder/index.html. Navigation will get quite confused if you refer to them as /folder/ or just /folder
  2. If you have a sub-item with the same url as another item, the site navigation will expand to display all items with that URL (when either is selected). All instances of the item will be highlighted.