function showhide(i) {
   var e = document.getElementById(i);
   //alert(e.id + ' = ' + e.style.visibility);
   e.style.color = "black";
   if (e.style.visibility == 'hidden') {
      e.style.visibility = 'visible';
   }
   else {
      e.style.visibility = 'hidden';
   }
}

function sh_control(link, ele) {
   var l = document.getElementById(link);
   var a = ele.substring(3);
   var t = '<a href="#' + a + '" onclick="showhide(\'' + ele + '\')">' +
           'Show/hide spoilers</a><br>';
   l.innerHTML = t;
}