title: AJAX, PHP, XML, and cascading drop-down lists
body: <p>What PHP libraries would you recommend to implement the following:</p>
  
  <ul>
  <li>Three dependent drop-down lists</li>
  <li>Three XML data sources</li>
  <li>AJAX-based</li>
  </ul>
  
  <p>Essentially, I'd like to create an XML database and wire up a form that allows the user to select three different dependent parameters:</p>
  
  <ol>
  <li>User clicks Region</li>
  <li>User clicks District (filtered by Region)</li>
  <li>User clicks Station (filtered by District)</li>
  </ol>
  
  <p>Even though I would like to use PHP and XML, the general problem is:</p>
  
  <ul>
  <li>One XHTML form</li>
  <li>Three dependent, cascading drop-down lists</li>
  <li>Three flat files (no relational database) for the list data</li>
  </ul>
  
  <p>The solution must be efficient, simple, reliable, and cross-browser.</p>
  
  <p>What technologies would you recommend to solve the problem?</p>
  
  <p>Thank you!</p>