function horizScroller(opt) {
  var d = 0;
  opt.delay = opt.delay || 50;
  opt.dist = opt.dist || 2;
  opt.leftEl.onmouseover = function() { d = -opt.dist; scroll(); }
  opt.leftEl.onmouseout = function() { d = 0 }
  opt.rightEl.onmouseover = function() { d = opt.dist; scroll(); }
  opt.rightEl.onmouseout = function() { d = 0 }
   
  function scroll() {
    if (!d) return;
    var x = opt.contentEl.scrollLeft+d, stop = false, rightBoundary = opt.contentEl.scrollWidth-opt.contentEl.offsetWidth;
    if (x<0) {
      addClassName(opt.leftEl, 'disabled');
      x = 0;
      stop = true;
    }
    else {
      removeClassName(opt.leftEl, 'disabled');
    }
    if (x>=rightBoundary) {
      addClassName(opt.rightEl, 'disabled');
      x = rightBoundary;
      stop = true;
    }
    else {
      removeClassName(opt.rightEl, 'disabled');
    }
    opt.contentEl.scrollLeft = x;
    if (stop) return;
    window.setTimeout(scroll, opt.delay);
  }
   
  function addClassName(el, className) {
    el.className = el.className.replace(new RegExp(' ?'+className+'|$'), ' '+className);
  }
   
  function removeClassName(el, className) {
    el.className = el.className.replace(new RegExp(' ?'+className+'( |$)'), '$1');
  }
}