function PageUI(dom){

	var self = this;
	self.dom = dom;

	self.pages = [];
	self.addPage = function(id, page){
		page.id = id;
		self.dom.appendChild(page.dom);
		self.pages.push(page);
	};
	self.currentPage = null;
	self.showPage = function(id){
		var shownPage = null;
		for(var i=0; i<self.pages.length; i++){
			var page = self.pages[i];
			if(page.id==id){
				page.show();
				shownPage = page;
			}else{
				page.hide();
			}
		}
		self.currentPage = shownPage;
		return shownPage;
	};

}
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PAGE UI: to extend to Sidebar, Play Controls, Modal.
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