var timeout         = 500;
var closetimer    = 0;
var ddmenuitem      = 0;

function jsddm_open()
{  jsddm_canceltimer();
  jsddm_close();
  ddmenuitem = $(this).find('ul').eq(0).css('visibility', 'visible');}

function jsddm_close()
{  if(ddmenuitem) ddmenuitem.css('visibility', 'hidden');}

function jsddm_timer()
{  closetimer = window.setTimeout(jsddm_close, timeout);}

function jsddm_canceltimer()
{  if(closetimer)
  {  window.clearTimeout(closetimer);
    closetimer = null;}}

$(document).ready(function()
{  $('#nav_main > ul > li').bind('mouseover', jsddm_open);
  $('#nav_main > ul > li').bind('mouseout',  jsddm_timer);});

document.onclick = jsddm_close;