/**
* function setup_image()
* メインコンテンツに、上下の画像を追加します。
* 
*   IN: {selector: CSS_CLASS_SELECTOR, before_image: PATH, after_image: PATH}
* 
*    ex. setup_paper({})
*        setup_paper({selector:"div.content", 
*                     before_image:"/images/content_bg_top_custom.gif", 
*                     after_image:"/images/content_bg_bottom_custom.gif"})
* 
**/
function setup_paper(args){
	var before_image_src = (typeof args.before_image == "undefined") ? "/images/content_bg_top.gif" : args.before_image;
	var after_image_src  = (typeof args.after_image == "undefined") ? "/images/content_bg_bottom.gif" : args.after_image;
	
	/* 該当する全てのタグの前後に、上下の画像を追加 */
	var selector = (typeof args.selector =="undefined") ? "div.paper" : args.selector;
	$$(selector).each(function(obj){
		new Insertion.Before(obj, create_image(before_image_src, "paper_top"));
		new Insertion.After(obj, create_image(after_image_src, "paper_bottom"));
	});
}

/* createElementは毎回しないといけないのでfunction内で作る */
function create_image(src, img_class){
	var img = document.createElement("img");
	img.src = src;
	img.className = img_class;
	return img;
}