<script type="text/javascript">
  function show(element) {
     var srcElement = document.getElementById(element);

     if(srcElement != null) {
        if(srcElement.style.display == "block") {
           srcElement.style.display= 'none';
        //srcElement.className = (trida=="r") ? "s" : "r";
        }
        else {
               srcElement.style.display='block';
        }
        return false;
     }
  }
</script>
<style>
#li
{
    display:none;
}

</style>

<ul>
<li><a href="#" onclick="show('li')" title="zobrazit">Main</a></li>


    <ul id="li">
        <li>XXX</li>
        <li>YYY</li>
    </ul>


<li>MAIN2</li>
<li>MAIN3</li>
</ul>