Código :
{foreach from=$data item=me}
<a id="showname" onclick="showname($id={$me.message_id});" >
<p>{$me.subject}</p>
</a>
<hr>
<p id="info" style="display: none">{$me.message}</p>
--JS--
{literal}
<script type="text/javascript" >
function showname(id) {
var showmessage = document.getElementById('showmessage');
var info = document.getElementById('info');
if(info.style.display == "block") {
info.style.display = "none";
}
</script>
Att. Gracias
