// initialize global DOM elements
var header;
var menu;
var tree;
var content;
var footer;
var submenu_file;
var submenu_edit;
var submenu_map;
function initDOM() {
	header			= document.getElementById('header');
	menu			= document.getElementById('menu');
	tree			= document.getElementById('tree_content');
	content			= document.getElementById('content');
	footer			= document.getElementById('footer');
	submenu_file	= document.getElementById('submenu_file');
	submenu_edit	= document.getElementById('submenu_edit');
	submenu_map		= document.getElementById('submenu_map');
}

// global variables