The `Boundary` element tool renders a rectangular border to show the bounding box of the element. It accepts a few additional argument, which can be passed as an object to the element tool constructor:

padding | number|object | This option determines whether the boundary area should be visually inflated and if so, by how much. Default is `10` (`{ left: 10, top: 10, right: 10, bottom: 10 }`).
rotate | boolean | Should the boundary rotate according to the element angle? Default is `false`.
useModelGeometry | boolean | If this option is set to `true`, the position of the boundary is calculated based on the dimensions of the element model.

Example:

    var boundaryTool = new joint.elementTools.Boundary({
        focusOpacity: 0.5,
        padding: 20,
        useModelGeometry: true
    });