function toggleNav(toggle){

	idToToggle = document.getElementById(toggle);
	mainNavID = 'main_nav';
	showNav = 'block_display';
	hideNav = 'no_display';
	
	if (idToToggle.className == showNav)  //If clicked item already showing, hide it and exit function.
	{
		idToToggle.className = hideNav;
		return false;
	};
	
	if (idToToggle.parentNode.parentNode.parentNode.id == mainNavID) //Toggle visible nav ULs when clicking highest level nav links.		
	{
		ulArray = document.getElementById(mainNavID).getElementsByTagName('ul').item(0).getElementsByTagName('ul'); //Collect all Uls in an array		
		for (var i=0;i<ulArray.length;i++) 
		{
				if (ulArray.item(i).className == showNav)
				{
					ulArray.item(i).className = hideNav;
				};				
		};
	};
	
	if (idToToggle.className == hideNav)  //Show item just clicked on.	
	{
		idToToggle.className = showNav;
	};
	
};