( function() {
	var container, button, menu, links, subMenus, i, len;
	container = document.getElementById( 'site-navigation' );
	if ( ! container ) {
		return;
	}
	
	menu = container.getElementsByTagName( 'ul' )[0];
	// Get all the link elements within the menu.
	links    = menu.getElementsByTagName( 'a' );
	subMenus = menu.getElementsByTagName( 'ul' );
	// Set menu items with submenus to aria-haspopup="true".
	for ( i = 0, len = subMenus.length; i < len; i++ ) {
		subMenus[i].parentNode.setAttribute( 'aria-haspopup', 'true' );
	}
	// Each time a menu link is focused or blurred, toggle focus.
	for ( i = 0, len = links.length; i < len; i++ ) {
		links[i].addEventListener( 'focus', toggleFocus, true );
		links[i].addEventListener( 'blur', toggleFocus, true );
	}
	/**
	 * Sets or removes .focus class on an element.
	 */
	function toggleFocus() {
		var self = this;
		// Move up through the ancestors of the current link until we hit .nav-menu.
		while ( -1 === self.className.indexOf( 'nav-menu' ) ) {
			// On li elements toggle the class .focus.
			if ( 'li' === self.tagName.toLowerCase() ) {
				if ( -1 !== self.className.indexOf( 'focus' ) ) {
					self.className = self.className.replace( ' focus', '' );
				} else {
					self.className += ' focus';
				}
			}
			self = self.parentElement;
		}
	}
	
} )();