function updateLabel(el,label)
{
  if (el.value==label) el.value = '';
  else if (el.value=='') el.value = label;
}

function navOn(nav)
{
  var image_src = nav.childNodes[0].src;
  if (image_src.indexOf('-on.') == -1)
  {
    var on_index = image_src.lastIndexOf('.');
    nav.childNodes[0].src = image_src.substring(0,on_index)+'-on'+image_src.substring(on_index);
  }
}

function navOff(nav)
{
  var image_src = nav.childNodes[0].src;
  var on_index = image_src.indexOf('-on.');
  if (on_index != -1)
  {
    nav.childNodes[0].src = image_src.substring(0,on_index)+image_src.substring(on_index+3);
  }
}

(function($) {
  var cache = [];
  // Arguments are image paths relative to the current page.
  $.preLoadImages = function() {
    var args_len = arguments.length;
    for (var i = args_len; i--;) {
      var cacheImage = document.createElement('img');
      cacheImage.src = arguments[i];
      cache.push(cacheImage);
    }
  }
})(jQuery);