function nav(e) {

  var o   = source(e);

  while(o && o.id.indexOf('nav') != 0) {
    o     = o.parentNode;

  }

  if( o.id ) {

    var s = document.getElementById(o.id.replace('nav', 'sub'));

    if( s ) {

      s.style.display = e.type == 'mouseover' ? 'block' : 'none';

    }

  }

} // ! nav()


function sub(e) {

  var o   = source(e);

  while(o && o.id.indexOf('sub') != 0) {
    o     = o.parentNode;

  }

  if( o.id ) {

    o.style.display = e.type == 'mouseover' ? 'block' : 'none';

    var n = document.getElementById(o.id.replace('sub', 'nav'));
        n.className = e.type == 'mouseover' ? 'active' : null;

  }

} // ! sub()


function nav_start() {

  var nav_list = document.getElementById('navigation').getElementsByTagName('ol');

  for(n = 0; n <= nav_list.length; n++) {

    if( n == 0 ) {

      listen(nav_list[n], 'mouseover', nav);
      listen(nav_list[n], 'mouseout',  nav);

    } else {

      listen(nav_list[n], 'mouseover', sub);
      listen(nav_list[n], 'mouseout',  sub);

    }

  }

}