done: function() {
                var mark = $('mark[data-markjs]').last();   // Scroll to last <mark>
                if (mark.length) {
                    $('html,body').animate({scrollTop: mark.offset().top-100}, 100);
                }
            }

if(e.which==13){ // 13 = enter key
            e.preventDefault();
            arrowOffset++;
        }