Well, I am forced to use Javascript due to I have to work with combo
boxes and I need "onchange" event to operate and select values
(depending of the option selected).

One combo box contains XML data and displays the values. When I select
one option, I need lo load one XML file (depending on the selected
value).

For example:

<select name="combo1">
<option select="file1.xml">Option1</option>
<option select="file2.xml">Option2</option>
<option select="file3.xml">Option3</option>
<option select="file4.xml">Option4</option>
</select>

<select name="combo1" onchange="transformSelection(this.value)">
  <option value="file1.xml">Option1</option>
...

best,
-Rob