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

padding | number | This option determines whether the boundary area should be visually inflated and if so, by how much. Default is `10`.

Example:

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