From Porcupine wiki

Developers: appendChild method

The appendChild appends a widget to the widgets collection. This is the method you should call if you want to dynamically add new widgets to you UI.

Syntax

widget.appendChild(oNewWidget);

Example

var lbl = new Label({
	height : '100%',
	left : 4,
	top : 2,
	width : 40,
	border : 1,
	caption : "A sample label"
});
widget.appendChild(lbl);