/**
                                 * Extends the dd-ddm-base Class to add support for the viewport shim to allow a draggable
                                 * anode to drag to be dragged over an iframe or any other node that traps mousemove events.
                                 * It is also required to have Drop Targets enabled, as the viewport shim will contain the shims for the Drop Targets.
                                 * @module dd
                                 * @submodule dd-ddm
                                 * @for DDM
                                 * @namespace DD
                                 */
                                Y.mix(Y.DD.DDM, {
                                    /**
                                    * The shim placed over the screen to track the mousemove event.
                                    * @private
                                    * @property _pg
                                    * @type {Node}
                                    */
                                    _pg: null,
                                    /**
                                    * Set this to true to set the shims opacity to .5 for debugging it, default: false.
                                    * @private
                                    * @property _debugShim
                                    * @type {Boolean}
                                    */
                                    _debugShim: false,
                                    _activateTargets: function() { },
                                    _deactivateTargets: function() {},
                                    _startDrag: function() {
                                        if (this.activeDrag && this.activeDrag.get('useShim')) {
                                            this._shimming = true;
                                            this._pg_activate();
                                            this._activateTargets();
                                        }
                                    },
                                    _endDrag: function() {
                                        Y.later(0, this, this._pg_deactivate);
                                        this._deactivateTargets();
                                    },
                                    /**
                                    * Deactivates the shim
                                    * @private
                                    * @method _pg_deactivate
                                    */
                                    _pg_deactivate: function() {
                                        this._pg.setStyle('display', 'none');
                                    },
                                    /**
                                    * Activates the shim
                                    * @private
                                    * @method _pg_activate
                                    */
                                    _pg_activate: function() {
                                        if (!this._pg) {
                                            this._createPG();
                                        }
                                        var ah = this.activeDrag.get('activeHandle'), cur = 'auto';
                                        if (ah) {
                                            cur = ah.getStyle('cursor');
                                        }
                                        if (cur === 'auto') {
                                            cur = this.get('dragCursor');
                                        }
                            
                                        this._pg_size();
                                        this._pg.setStyles({
                                            top: 0,
                                            left: 0,
                                            display: 'block',
                                            opacity: ((this._debugShim) ? '.5' : '0'),
                                            cursor: cur
                                        });
                                    },
                                    /**
                                    * Sizes the shim on: activatation, window:scroll, window:resize
                                    * @private
                                    * @method _pg_size
                                    */
                                    _pg_size: function() {
                                        if (this.activeDrag) {
                                            var b = Y.one('body'),
                                            h = b.get('docHeight'),
                                            w = b.get('docWidth');
                                            this._pg.setStyles({
                                                height: h + 'px',
                                                width: w + 'px'
                                            });
                                        }
                                    },
                                    /**
                                    * Creates the shim and adds it's listeners to it.
                                    * @private
                                    * @method _createPG
                                    */
                                    _createPG: function() {
                                        var pg = Y.Node.create('<div></div>'),
                                        bd = Y.one('body'), win;
                                        pg.setStyles({
                                            top: '0',
                                            left: '0',
                                            position: 'absolute',
                                            zIndex: '99999',
                                            overflow: 'hidden',
                                            backgroundColor: 'red',
                                            display: 'none',
                                            height: '5px',
                                            width: '5px'
                                        });
                                        pg.set('id', Y.stamp(pg));
                                        pg.addClass(Y.DD.DDM.CSS_PREFIX + '-shim');
                                        bd.prepend(pg);
                                        this._pg = pg;
                                        this._pg.on('mousemove', Y.throttle(Y.bind(this._move, this), this.get('throttleTime')));
                                        this._pg.on('mouseup', Y.bind(this._end, this));
                            
                                        win = Y.one('win');
                                        Y.on('window:resize', Y.bind(this._pg_size, this));
                                        win.on('scroll', Y.bind(this._pg_size, this));
                                    }
                                }, true);