The source code

    /**
     * @class Ext.state.Provider
     * Abstract base class for state provider implementations. This class provides methods
     * for encoding and decoding <b>typed</b> variables including dates and defines the
     * Provider interface.
     */
    Ext.state.Provider = Ext.extend(Ext.util.Observable, {

        constructor : 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);
        },

        /**
         * 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){
            /**
             * a -> Array
             * n -> Number
             * d -> Date
             * b -> Boolean
             * s -> String
             * o -> Object
             * -> Empty (null)
             */
            var re = /^(a|n|d|b|s|o|e)\:(.*)$/,
                matches = re.exec(unescape(cookie)),
                all,
                type,
                v,
                kv;
            if(!matches || !matches[1]){
                return; // non state cookie
            }
            type = matches[1];
            v = matches[2];
            switch(type){
                case 'e':
                    return null;
                case 'n':
                    return parseFloat(v);
                case 'd':
                    return new Date(Date.parse(v));
                case 'b':
                    return (v == '1');
                case 'a':
                    all = [];
                    if(v != ''){
                        Ext.each(v.split('^'), function(val){
                            all.push(this.decodeValue(val));
                        }, this);
                    }
                    return all;
               case 'o':
                    all = {};
                    if(v != ''){
                        Ext.each(v.split('^'), function(val){
                            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,
                flat = '',
                i = 0,
                len,
                key;
            if(v == null){
                return 'e:1';
            }else 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)){
                for(len = v.length; i < len; i++){
                    flat += this.encodeValue(v[i]);
                    if(i != len - 1){
                        flat += '^';
                    }
                }
                enc = 'a:' + flat;
            }else if(typeof v == 'object'){
                for(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);
        }
    });