function zebra_streifen(tablename, style) {
  var table = document.getElementById(tablename); 
  if (!table) return;
  var tbodies = table.getElementsByTagName('tbody');
  for (var h=0; h<tbodies.length; h++) {
   var even = true;
   var trs = tbodies[h].getElementsByTagName('tr');
   for (var i=0; i<trs.length; i++) {
    trs[i].onmouseover = function() { this.className += ' '+style+'ruled'; return false }
    trs[i].onmouseout = function() { this.className = this.className.replace(style+'ruled', ''); return false }
    if (even) trs[i].className += ' '+style+'even';
    even = !even;
   }
  }
}