title: Force html field value from ajax drop down and not user input
body: <p>I have a field which produces a drop down that a user can select from as such</p>
  
  <pre><code>            $(function() {
                $('.serial_number').live('focus.autocomplete', function() { 
                  $(this).autocomplete("/admin/includes/getinvoiceajax.php", {
                      width: 300,
                      matchContains: true,
                      mustMatch: true,
                      selectFirst: false
                  }); 
                });
              });
  
  &lt;input type="text" name="serial_number[]" id="serial_number" class="serial_number" /&gt;
  &lt;input type="text" name="serial_number[]" id="serial_number" class="serial_number" /&gt;
  &lt;input type="text" name="serial_number[]" id="serial_number" class="serial_number" /&gt;
  &lt;input type="text" name="serial_number[]" id="serial_number" class="serial_number" /&gt;
  </code></pre>
  
  <p>I have set the mustMatch: true, so a user can only select what is from the dropdown list. Is there a way to not allow a duplicate selection from any of the other fields. Since I have a few of these fields it could possible allow the user to select the same value for multiple fields. I need to make sure they are unique.</p>