//=============================================================================
// Globals
//=============================================================================
var S_SELECTED = "selected";
var S_HOVER = "hover"

var last_menu_item = {obj: null};
var objText = null;

function Init()
{
    objText = document.getElementById('right_column');
    
    AddListHover( document.getElementById("menu") )  
    
   // Show default selection
   SelectMenuItem(document.getElementById('menu_default'), 'introduction');
}

function SelectMenuItem(menu_item, selection)
{
    ShowText(selection);
    ModifyGroupElement(last_menu_item, menu_item, S_SELECTED);
}

function ShowText(element_id)
{
    var obj = document.getElementById(element_id);
    if (obj != null && objText!= null)
    {
        objText.innerHTML = obj.innerHTML;
    }
}

function ModifyGroupElement(last_element, element, class_name)
{
    if (last_element.obj) 
        last_element.obj.className = last_element.obj.className.replace(class_name, "");
    
    if (element != null)
        element.className += " " + class_name;  

    last_element.obj = element;
}

function AddListHover(list)
{    
  var nodes = list.getElementsByTagName("li");
  for (var i=0; i < nodes.length; i++) 
  {
    nodes[i].onmouseover = function() 
    { 
      if (this.className != S_SELECTED)
      {
        this.className += " " + S_HOVER; 
      }    
    }
    
    nodes[i].onmouseout = function() 
    { 
        this.className = this.className.replace(S_HOVER, ""); 
    }
  }
}