The source code

    /**
     * @ignore
     * position and visible extension，可定位的隐藏层
     * @author yiminghe@gmail.com
     */
    KISSY.add("component/extension/position", function (S) {

        /**
         * @class KISSY.Component.Extension.Position
         * Position extension class. Make component positionable.
         */
        function Position() {
        }

        Position.ATTRS = {
            /**
             * Horizontal axis
             * @type {Number}
             * @property x
             */
            /**
             * Horizontal axis
             * @cfg {Number} x
             */
            /**
             * @ignore
             */
            x: {
                view: 1
            },

            /**
             * Vertical axis
             * @type {Number}
             * @property y
             */
            /**
             * Vertical axis
             * @cfg {Number} y
             */
            /**
             * @ignore
             */
            y: {
                view: 1
            },
            /**
             * Horizontal and vertical axis.
             * @ignore
             * @type {Number[]}
             */
            xy: {
                // 相对 page 定位, 有效值为 [n, m], 为 null 时, 选 align 设置
                setter: function (v) {
                    var self = this,
                        xy = S.makeArray(v);
                    /*
                     属性内分发特别注意：
                     xy -> x,y
                     */
                    if (xy.length) {
                        xy[0] && self.set("x", xy[0]);
                        xy[1] && self.set("y", xy[1]);
                    }
                    return v;
                },

                // xy 纯中转作用
                getter: function () {
                    return [this.get("x"), this.get("y")];
                }
            },

            /**
             * z-index value.
             * @type {Number}
             * @property zIndex
             */
            /**
             * z-index value.
             * @cfg {Number} zIndex
             */
            /**
             * @ignore
             */
            zIndex: {
                view: 1
            },
            /**
             * Positionable element is by default visible false.
             * For compatibility in overlay and PopupMenu.
             *
             * Defaults to: false
             *
             * @ignore
             */
            visible: {
                value: false
            }
        };

        Position.prototype = {
            /**
             * Move to absolute position.
             * @ignore
             * @chainable
             */
            move: function (x, y) {
                var self = this;
                if (S.isArray(x)) {
                    y = x[1];
                    x = x[0];
                }
                self.set("xy", [x, y]);
                return self;
            }
        };

        return Position;
    });