Help me to understand parts of a template code

1

Please help me to understand this template of a navigation menu.

I have made comments in the code on things I especially don’t understand.

The template can be downloaded here: (the speaker template). http://www.flashmo.com/preview/flashmo_086_speaker

menu_item_group is a MC.
menu_item is a MC nested inside of menu_item_group.
item_label is a dynamic text field nested inside of menu_item.

menu_item_group.menu_item._visible = false;
var menu_label:Array = new Array("Home", "News", "Portfolio", "Awards", "Company", "Contact");
var total:Number = menu_label.length;
var distance_x:Number = 82;
var i:Number = 0;

for( ; i < total; i++ )        
{
    menu_item_group.menu_item.duplicateMovieClip("menu_item"+i, i);
    menu_item_group["menu_item"+i].over = true;                                // what is .over ?   If i=1 is ["menu_item" + i]  equal to .menu_item1 then ?
    menu_item_group["menu_item"+i].item_label = menu_label*;                // is the instancename changed here or what ? (item_label is a dynamic text field)
    menu_item_group["menu_item"+i].item_no = i;                                // what is item_no ? I can't find any movieclip called item_no in this template.
    menu_item_group["menu_item"+i]._x = i * distance_x;
}
function change_page(no):Void                                                // what happens here? Is change_page a function built into AS ?
{
    for( i = 0; i < total; i++ )
    {
        menu_item_group["menu_item"+i].flashmo_button._visible = true;
        menu_item_group["menu_item"+i].over = true;
        menu_item_group["menu_item"+i].flashmo_button.onRollOver = function() 
        {
            this._parent.over = false;                                        // What happens here? What does _parent refer to ?
        }
        menu_item_group["menu_item"+i].flashmo_button.onRollOut = menu_item_group["menu_item"+i].flashmo_button.onDragOut = function() 
        {
            this._parent.over = true;
        }
        menu_item_group["menu_item"+i].flashmo_button.onRelease = function() 
        {
            _root.change_page(this._parent.item_no);
        }
        menu_item_group["menu_item"+i].onEnterFrame = function() 
        {
            if( this.over == true ) this.prevFrame();
            else this.nextFrame();
        }
    }
    delete menu_item_group["menu_item"+no].flashmo_button.onRollOut;        // what is "no" ?
    menu_item_group["menu_item"+no].flashmo_button._visible = false;
    menu_item_group["menu_item"+no].over = false;
    _root.page = no + 1;
    _root.play();
}
change_page(0);