    static let eraser = AttributesStream.ToolStyle(width: 10, color: nil)

    lazy var attributeStream = { () -> AttributesStream in
        let attributeStream = AttributesStream()
        attributeStream.styleOverride = { delta in
            switch delta {
            case .addedBezierPath(let index):
                return index == 0 ? Self.pen : Self.eraser
            default: