The source code

    Ext.ns('Ext.ux.form');

    /**
     * @class Ext.ux.form.MultiSelect
     * @extends Ext.form.Field
     * A control that allows selection and form submission of multiple list items.
     *
     *  @history
     *    2008-06-19 bpm Original code contributed by Toby Stuart (with contributions from Robert Williams)
     *    2008-06-19 bpm Docs and demo code clean up
     *
     * @constructor
     * Create a new MultiSelect
     * @param {Object} config Configuration options
     * @xtype multiselect
     */
    Ext.ux.form.MultiSelect = Ext.extend(Ext.form.Field,  {
        /**
         * @cfg {String} legend Wraps the object with a fieldset and specified legend.
         */
        /**
         * @cfg {Ext.ListView} view The {@link Ext.ListView} used to render the multiselect list.
         */
        /**
         * @cfg {String/Array} dragGroup The ddgroup name(s) for the MultiSelect DragZone (defaults to undefined).
         */
        /**
         * @cfg {String/Array} dropGroup The ddgroup name(s) for the MultiSelect DropZone (defaults to undefined).
         */
        /**
         * @cfg {Boolean} ddReorder Whether the items in the MultiSelect list are drag/drop reorderable (defaults to false).
         */
        ddReorder:false,
        /**
         * @cfg {Object/Array} tbar The top toolbar of the control. This can be a {@link Ext.Toolbar} object, a
         * toolbar config, or an array of buttons/button configs to be added to the toolbar.
         */
        /**
         * @cfg {String} appendOnly True if the list should only allow append drops when drag/drop is enabled
         * (use for lists which are sorted, defaults to false).
         */
        appendOnly:false,
        /**
         * @cfg {Number} width Width in pixels of the control (defaults to 100).
         */
        width:100,
        /**
         * @cfg {Number} height Height in pixels of the control (defaults to 100).
         */
        height:100,
        /**
         * @cfg {String/Number} displayField Name/Index of the desired display field in the dataset (defaults to 0).
         */
        displayField:0,
        /**
         * @cfg {String/Number} valueField Name/Index of the desired value field in the dataset (defaults to 1).
         */
        valueField:1,
        /**
         * @cfg {Boolean} allowBlank False to require at least one item in the list to be selected, true to allow no
         * selection (defaults to true).
         */
        allowBlank:true,
        /**
         * @cfg {Number} minSelections Minimum number of selections allowed (defaults to 0).
         */
        minSelections:0,
        /**
         * @cfg {Number} maxSelections Maximum number of selections allowed (defaults to Number.MAX_VALUE).
         */
        maxSelections:Number.MAX_VALUE,
        /**
         * @cfg {String} blankText Default text displayed when the control contains no items (defaults to the same value as
         * {@link Ext.form.TextField#blankText}.
         */
        blankText:Ext.form.TextField.prototype.blankText,
        /**
         * @cfg {String} minSelectionsText Validation message displayed when {@link #minSelections} is not met (defaults to 'Minimum {0}
         * item(s) required').  The {0} token will be replaced by the value of {@link #minSelections}.
         */
        minSelectionsText:'Minimum {0} item(s) required',
        /**
         * @cfg {String} maxSelectionsText Validation message displayed when {@link #maxSelections} is not met (defaults to 'Maximum {0}
         * item(s) allowed').  The {0} token will be replaced by the value of {@link #maxSelections}.
         */
        maxSelectionsText:'Maximum {0} item(s) allowed',
        /**
         * @cfg {String} delimiter The string used to delimit between items when set or returned as a string of values
         * (defaults to ',').
         */
        delimiter:',',
        /**
         * @cfg {Ext.data.Store/Array} store The data source to which this MultiSelect is bound (defaults to undefined).
         * Acceptable values for this property are:
         *
         * any {@link Ext.data.Store Store} subclass
         * an Array : Arrays will be converted to a {@link Ext.data.ArrayStore} internally.
         *
         * 1-dimensional array : (e.g., ['Foo','Bar'])
         * A 1-dimensional array will automatically be expanded (each array item will be the combo
         * {@link #valueField value} and {@link #displayField text})
         * 2-dimensional array : (e.g., [['f','Foo'],['b','Bar']])
         * For a multi-dimensional array, the value in index 0 of each item will be assumed to be the combo
         * {@link #valueField value}, while the value at index 1 is assumed to be the combo {@link #displayField text}.
         *
         */

        // private
        defaultAutoCreate : {tag: "div"},

        // private
        initComponent: function(){
            Ext.ux.form.MultiSelect.superclass.initComponent.call(this);

            if(Ext.isArray(this.store)){
                if (Ext.isArray(this.store[0])){
                    this.store = new Ext.data.ArrayStore({
                        fields: ['value','text'],
                        data: this.store
                    });
                    this.valueField = 'value';
                }else{
                    this.store = new Ext.data.ArrayStore({
                        fields: ['text'],
                        data: this.store,
                        expandData: true
                    });
                    this.valueField = 'text';
                }
                this.displayField = 'text';
            } else {
                this.store = Ext.StoreMgr.lookup(this.store);
            }

            this.addEvents({
                'dblclick' : true,
                'click' : true,
                'change' : true,
                'drop' : true
            });
        },

        // private
        onRender: function(ct, position){
            Ext.ux.form.MultiSelect.superclass.onRender.call(this, ct, position);

            var fs = this.fs = new Ext.form.FieldSet({
                renderTo: this.el,
                title: this.legend,
                height: this.height,
                width: this.width,
                style: "padding:0;",
                tbar: this.tbar,
                bodyStyle: 'overflow: auto;'
            });

            this.view = new Ext.ListView({
                multiSelect: true,
                store: this.store,
                columns: [{ header: 'Value', width: 1, dataIndex: this.displayField }],
                hideHeaders: true
            });

            fs.add(this.view);

            this.view.on('click', this.onViewClick, this);
            this.view.on('beforeclick', this.onViewBeforeClick, this);
            this.view.on('dblclick', this.onViewDblClick, this);

            this.hiddenName = this.name || Ext.id();
            var hiddenTag = { tag: "input", type: "hidden", value: "", name: this.hiddenName };
            this.hiddenField = this.el.createChild(hiddenTag);
            this.hiddenField.dom.disabled = this.hiddenName != this.name;
            fs.doLayout();
        },

        // private
        afterRender: function(){
            Ext.ux.form.MultiSelect.superclass.afterRender.call(this);

            if (this.ddReorder && !this.dragGroup && !this.dropGroup){
                this.dragGroup = this.dropGroup = 'MultiselectDD-' + Ext.id();
            }

            if (this.draggable || this.dragGroup){
                this.dragZone = new Ext.ux.form.MultiSelect.DragZone(this, {
                    ddGroup: this.dragGroup
                });
            }
            if (this.droppable || this.dropGroup){
                this.dropZone = new Ext.ux.form.MultiSelect.DropZone(this, {
                    ddGroup: this.dropGroup
                });
            }
        },

        // private
        onViewClick: function(vw, index, node, e) {
            this.fireEvent('change', this, this.getValue(), this.hiddenField.dom.value);
            this.hiddenField.dom.value = this.getValue();
            this.fireEvent('click', this, e);
            this.validate();
        },

        // private
        onViewBeforeClick: function(vw, index, node, e) {
            if (this.disabled) {return false;}
        },

        // private
        onViewDblClick : function(vw, index, node, e) {
            return this.fireEvent('dblclick', vw, index, node, e);
        },

        /**
         * Returns an array of data values for the selected items in the list. The values will be separated
         * by {@link #delimiter}.
         * @return {Array} value An array of string data values
         */
        getValue: function(valueField){
            var returnArray = [];
            var selectionsArray = this.view.getSelectedIndexes();
            if (selectionsArray.length == 0) {return '';}
            for (var i=0; i/**
         * Sets a delimited string (using {@link #delimiter}) or array of data values into the list.
         * @param {String/Array} values The values to set
         */
        setValue: function(values) {
            var index;
            var selections = [];
            this.view.clearSelections();
            this.hiddenField.dom.value = '';

            if (!values || (values == '')) { return; }

            if (!Ext.isArray(values)) { values = values.split(this.delimiter); }
            for (var i=0; i this.maxSelections) {
                this.markInvalid(String.format(this.maxSelectionsText, this.maxSelections));
                return false;
            }
            return true;
        },

        // inherit docs
        disable: function(){
            this.disabled = true;
            this.hiddenField.dom.disabled = true;
            this.fs.disable();
        },

        // inherit docs
        enable: function(){
            this.disabled = false;
            this.hiddenField.dom.disabled = false;
            this.fs.enable();
        },

        // inherit docs
        destroy: function(){
            Ext.destroy(this.fs, this.dragZone, this.dropZone);
            Ext.ux.form.MultiSelect.superclass.destroy.call(this);
        }
    });

    Ext.reg('multiselect', Ext.ux.form.MultiSelect);

    //backwards compat
    Ext.ux.Multiselect = Ext.ux.form.MultiSelect;

    Ext.ux.form.MultiSelect.DragZone = function(ms, config){
        this.ms = ms;
        this.view = ms.view;
        var ddGroup = config.ddGroup || 'MultiselectDD';
        var dd;
        if (Ext.isArray(ddGroup)){
            dd = ddGroup.shift();
        } else {
            dd = ddGroup;
            ddGroup = null;
        }
        Ext.ux.form.MultiSelect.DragZone.superclass.constructor.call(this, this.ms.fs.body, { containerScroll: true, ddGroup: dd });
        this.setDraggable(ddGroup);
    };

    Ext.extend(Ext.ux.form.MultiSelect.DragZone, Ext.dd.DragZone, {
        onInitDrag : function(x, y){
            var el = Ext.get(this.dragData.ddel.cloneNode(true));
            this.proxy.update(el.dom);
            el.setWidth(el.child('em').getWidth());
            this.onStartDrag(x, y);
            return true;
        },

        // private
        collectSelection: function(data) {
            data.repairXY = Ext.fly(this.view.getSelectedNodes()[0]).getXY();
            var i = 0;
            this.view.store.each(function(rec){
                if (this.view.isSelected(i)) {
                    var n = this.view.getNode(i);
                    var dragNode = n.cloneNode(true);
                    dragNode.id = Ext.id();
                    data.ddel.appendChild(dragNode);
                    data.records.push(this.view.store.getAt(i));
                    data.viewNodes.push(n);
                }
                i++;
            }, this);
        },

        // override
        onEndDrag: function(data, e) {
            var d = Ext.get(this.dragData.ddel);
            if (d && d.hasClass("multi-proxy")) {
                d.remove();
            }
        },

        // override
        getDragData: function(e){
            var target = this.view.findItemFromChild(e.getTarget());
            if(target) {
                if (!this.view.isSelected(target) && !e.ctrlKey && !e.shiftKey) {
                    this.view.select(target);
                    this.ms.setValue(this.ms.getValue());
                }
                if (this.view.getSelectionCount() == 0 || e.ctrlKey || e.shiftKey) return false;
                var dragData = {
                    sourceView: this.view,
                    viewNodes: [],
                    records: []
                };
                if (this.view.getSelectionCount() == 1) {
                    var i = this.view.getSelectedIndexes()[0];
                    var n = this.view.getNode(i);
                    dragData.viewNodes.push(dragData.ddel = n);
                    dragData.records.push(this.view.store.getAt(i));
                    dragData.repairXY = Ext.fly(n).getXY();
                } else {
                    dragData.ddel = document.createElement('div');
                    dragData.ddel.className = 'multi-proxy';
                    this.collectSelection(dragData);
                }
                return dragData;
            }
            return false;
        },

        // override the default repairXY.
        getRepairXY : function(e){
            return this.dragData.repairXY;
        },

        // private
        setDraggable: function(ddGroup){
            if (!ddGroup) return;
            if (Ext.isArray(ddGroup)) {
                Ext.each(ddGroup, this.setDraggable, this);
                return;
            }
            this.addToGroup(ddGroup);
        }
    });

    Ext.ux.form.MultiSelect.DropZone = function(ms, config){
        this.ms = ms;
        this.view = ms.view;
        var ddGroup = config.ddGroup || 'MultiselectDD';
        var dd;
        if (Ext.isArray(ddGroup)){
            dd = ddGroup.shift();
        } else {
            dd = ddGroup;
            ddGroup = null;
        }
        Ext.ux.form.MultiSelect.DropZone.superclass.constructor.call(this, this.ms.fs.body, { containerScroll: true, ddGroup: dd });
        this.setDroppable(ddGroup);
    };

    Ext.extend(Ext.ux.form.MultiSelect.DropZone, Ext.dd.DropZone, {
        /**
    	 * Part of the Ext.dd.DropZone interface. If no target node is found, the
    	 * whole Element becomes the target, and this causes the drop gesture to append.
    	 */
        getTargetFromEvent : function(e) {
            var target = e.getTarget();
            return target;
        },

        // private
        getDropPoint : function(e, n, dd){
            if (n == this.ms.fs.body.dom) { return "below"; }
            var t = Ext.lib.Dom.getY(n), b = t + n.offsetHeight;
            var c = t + (b - t) / 2;
            var y = Ext.lib.Event.getPageY(e);
            if(y <= c) {
                return "above";
            }else{
                return "below";
            }
        },

        // private
        isValidDropPoint: function(pt, n, data) {
            if (!data.viewNodes || (data.viewNodes.length != 1)) {
                return true;
            }
            var d = data.viewNodes[0];
            if (d == n) {
                return false;
            }
            if ((pt == "below") && (n.nextSibling == d)) {
                return false;
            }
            if ((pt == "above") && (n.previousSibling == d)) {
                return false;
            }
            return true;
        },

        // override
        onNodeEnter : function(n, dd, e, data){
            return false;
        },

        // override
        onNodeOver : function(n, dd, e, data){
            var dragElClass = this.dropNotAllowed;
            var pt = this.getDropPoint(e, n, dd);
            if (this.isValidDropPoint(pt, n, data)) {
                if (this.ms.appendOnly) {
                    return "x-tree-drop-ok-below";
                }

                // set the insert point style on the target node
                if (pt) {
                    var targetElClass;
                    if (pt == "above"){
                        dragElClass = n.previousSibling ? "x-tree-drop-ok-between" : "x-tree-drop-ok-above";
                        targetElClass = "x-view-drag-insert-above";
                    } else {
                        dragElClass = n.nextSibling ? "x-tree-drop-ok-between" : "x-tree-drop-ok-below";
                        targetElClass = "x-view-drag-insert-below";
                    }
                    if (this.lastInsertClass != targetElClass){
                        Ext.fly(n).replaceClass(this.lastInsertClass, targetElClass);
                        this.lastInsertClass = targetElClass;
                    }
                }
            }
            return dragElClass;
        },

        // private
        onNodeOut : function(n, dd, e, data){
            this.removeDropIndicators(n);
        },

        // private
        onNodeDrop : function(n, dd, e, data){
            if (this.ms.fireEvent("drop", this, n, dd, e, data) === false) {
                return false;
            }
            var pt = this.getDropPoint(e, n, dd);
            if (n != this.ms.fs.body.dom)
                n = this.view.findItemFromChild(n);
            var insertAt = (this.ms.appendOnly || (n == this.ms.fs.body.dom)) ? this.view.store.getCount() : this.view.indexOf(n);
            if (pt == "below") {
                insertAt++;
            }

            var dir = false;

            // Validate if dragging within the same MultiSelect
            if (data.sourceView == this.view) {
                // If the first element to be inserted below is the target node, remove it
                if (pt == "below") {
                    if (data.viewNodes[0] == n) {
                        data.viewNodes.shift();
                    }
                } else {  // If the last element to be inserted above is the target node, remove it
                    if (data.viewNodes[data.viewNodes.length - 1] == n) {
                        data.viewNodes.pop();
                    }
                }

                // Nothing to drop...
                if (!data.viewNodes.length) {
                    return false;
                }

                // If we are moving DOWN, then because a store.remove() takes place first,
                // the insertAt must be decremented.
                if (insertAt > this.view.store.indexOf(data.records[0])) {
                    dir = 'down';
                    insertAt--;
                }
            }

            for (var i = 0; i < data.records.length; i++) {
                var r = data.records[i];
                if (data.sourceView) {
                    data.sourceView.store.remove(r);
                }
                this.view.store.insert(dir == 'down' ? insertAt : insertAt++, r);
                var si = this.view.store.sortInfo;
                if(si){
                    this.view.store.sort(si.field, si.direction);
                }
            }
            return true;
        },

        // private
        removeDropIndicators : function(n){
            if(n){
                Ext.fly(n).removeClass([
                    "x-view-drag-insert-above",
                    "x-view-drag-insert-left",
                    "x-view-drag-insert-right",
                    "x-view-drag-insert-below"]);
                this.lastInsertClass = "_noclass";
            }
        },

        // private
        setDroppable: function(ddGroup){
            if (!ddGroup) return;
            if (Ext.isArray(ddGroup)) {
                Ext.each(ddGroup, this.setDroppable, this);
                return;
            }
            this.addToGroup(ddGroup);
        }
    });