function tv(id) { 
  /*toggle visibility*/
  var to_toggle = document.getElementById(id);
  if(to_toggle.className == 'cbox_closed') {
    /* Close the other comment boxes and open this one */
    var doc = document.getElementsByTagName("span");
    for (var i=0; i<doc.length; i++) {
      if (doc[i].className == 'cbox_open') {
        doc[i].className = 'cbox_closed';
      }
    }
    to_toggle.className = 'cbox_open';
  }
  else if(to_toggle.className == 'cbox_open') {
    /* Close this comment box */
    to_toggle.className= 'cbox_closed';
  }
}