var timeout	= 500;
      var closetimer	= 0;
      var ddmenuitem	= 0;
      
      // open hidden layer
      function mopen(id)
      {	
      	// cancel close timer
      	mcancelclosetime();
      
      	// close old layer
      	if(ddmenuitem) ddmenuitem.style.visibility = 'hidden';
      
      	// get new layer and show it
      	ddmenuitem = document.getElementById(id);
      	ddmenuitem.style.visibility = 'visible';
      
      }
      // close showed layer
      function mclose()
      {
      	if(ddmenuitem) ddmenuitem.style.visibility = 'hidden';
      }
      
      // go close timer
      function mclosetime()
      {
      	closetimer = window.setTimeout(mclose, timeout);
      }
      
      // cancel close timer
      function mcancelclosetime()
      {
      	if(closetimer)
      	{
      		window.clearTimeout(closetimer);
      		closetimer = null;
      	}
      }
      
      // close layer when click-out
      document.onclick = mclose;