line: function(parent, x1, y1, x2, y2, settings) {
        var args = this._args(arguments, ['x1', 'y1', 'x2', 'y2']);
        return this._makeNode(args.parent, 'line', $.extend(
            {x1: args.x1, y1: args.y1, x2: args.x2, y2: args.y2}, args.settings || {}));
    },