The source code

    /*!
     * Ext JS Library 3.2.1
     * Copyright(c) 2006-2010 Ext JS, Inc.
     * licensing@extjs.com
     * http://www.extjs.com/license
     */
    /**
     * @class Ext.state.Provider
     * Abstract base class for state provider implementations. This class provides methods
     * for encoding and decoding typed variables including dates and defines the
     * Provider interface.
     */
    Ext.state.Provider = function(){
        /**
         * @event statechange
         * Fires when a state change occurs.
         * @param {Provider} this This state provider
         * @param {String} key The state key which was changed
         * @param {String} value The encoded value for the state
         */
        this.addEvents("statechange");
        this.state = {};
        Ext.state.Provider.superclass.constructor.call(this);
    };
    Ext.extend(Ext.state.Provider, Ext.util.Observable, {
        /**
         * Returns the current value for a key
         * @param {String} name The key name
         * @param {Mixed} defaultValue A default value to return if the key's value is not found
         * @return {Mixed} The state data
         */
        get : function(name, defaultValue){
            return typeof this.state[name] == "undefined" ?
                defaultValue : this.state[name];
        },

        /**
         * Clears a value from the state
         * @param {String} name The key name
         */
        clear : function(name){
            delete this.state[name];
            this.fireEvent("statechange", this, name, null);
        },

        /**
         * Sets the value for a key
         * @param {String} name The key name
         * @param {Mixed} value The value to set
         */
        set : function(name, value){
            this.state[name] = value;
            this.fireEvent("statechange", this, name, value);
        },

        /**
         * Decodes a string previously encoded with {@link #encodeValue}.
         * @param {String} value The value to decode
         * @return {Mixed} The decoded value
         */
        decodeValue : function(cookie){
            var re = /^(a|n|d|b|s|o)\:(.*)$/;
            var matches = re.exec(unescape(cookie));
            if(!matches || !matches[1]) return; // non state cookie
            var type = matches[1];
            var v = matches[2];
            switch(type){
                case "n":
                    return parseFloat(v);
                case "d":
                    return new Date(Date.parse(v));
                case "b":
                    return (v == "1");
                case "a":
                    var all = [];
                    if(v != ''){
                        Ext.each(v.split('^'), function(val){
                            all.push(this.decodeValue(val));
                        }, this);
                    }
                    return all;
               case "o":
                    var all = {};
                    if(v != ''){
                        Ext.each(v.split('^'), function(val){
                            var kv = val.split('=');
                            all[kv[0]] = this.decodeValue(kv[1]);
                        }, this);
                    }
                    return all;
               default:
                    return v;
            }
        },

        /**
         * Encodes a value including type information.  Decode with {@link #decodeValue}.
         * @param {Mixed} value The value to encode
         * @return {String} The encoded value
         */
        encodeValue : function(v){
            var enc;
            if(typeof v == "number"){
                enc = "n:" + v;
            }else if(typeof v == "boolean"){
                enc = "b:" + (v ? "1" : "0");
            }else if(Ext.isDate(v)){
                enc = "d:" + v.toGMTString();
            }else if(Ext.isArray(v)){
                var flat = "";
                for(var i = 0, len = v.length; i < len; i++){
                    flat += this.encodeValue(v[i]);
                    if(i != len-1) flat += "^";
                }
                enc = "a:" + flat;
            }else if(typeof v == "object"){
                var flat = "";
                for(var key in v){
                    if(typeof v[key] != "function" && v[key] !== undefined){
                        flat += key + "=" + this.encodeValue(v[key]) + "^";
                    }
                }
                enc = "o:" + flat.substring(0, flat.length-1);
            }else{
                enc = "s:" + v;
            }
            return escape(enc);
        }
    });