var displayed = null;

var LINK = "_link";

(function()
{
  if (window.addEventListener)
  {
    window.addEventListener("load", setup_drop_down_menu, false);    
  }
  else
  {
    window.attachEvent("onload", setup_drop_down_menu);
  }
})();

function setup_drop_down_menu()
{
  var divs = document.getElementById("navigation_menu").getElementsByTagName("div");
  
  for (var i = 0; i < divs.length; i++)
  {    
    setup_link(divs[i].id);
  }
}

function setup_link(div_id)
{
  var link = document.getElementById(div_id + LINK);
  
  link.onmousemove = function(){display_menu(div_id);};
  link.onmouseout = function(){hide_displayed_menu();}
  link.onclick = function(){hide_displayed_menu();} 
}

function hide_displayed_menu()
{
  if (displayed)
  {
    displayed.style.display = 'none';
    displayed = null;
  }
}

function display_menu(id)
{
  hide_displayed_menu();

  displayed = document.getElementById(id);
  displayed.style.display = 'block';
  
  displayed.onmouseover = function(){display_menu(id);};
  displayed.onmouseout = function(){hide_displayed_menu();};    
  displayed.onclick = function(){hide_displayed_menu();};
}