[
  { "id" : "manager", "type" : "ClutterBoxLayout" },

  {
    "id" : "container", "type" : "ClutterBox",
    "layout-manager" : "manager",
    "children" : [
      {
        "id" : "actor", "type" : "ClutterRectangle",
        "layout::x-fill" : true,
        "layout::y-align" : "center",
        "layout::expand" : true
      }
    ]
  }
]