The source code

    /**
     * @class Ext.AbstractManager
     * @extends Object
     * Base Manager class - extended by ComponentMgr and PluginMgr
     */
    Ext.AbstractManager = Ext.extend(Object, {
        typeName: 'type',

        constructor: function(config) {
            Ext.apply(this, config || {});

            /**
             * Contains all of the items currently managed
             * @property all
             * @type Ext.util.MixedCollection
             */
            this.all = new Ext.util.MixedCollection();

            this.types = {};
        },

        /**
         * Returns a component by {@link Ext.Component#id id}.
         * For additional details see {@link Ext.util.MixedCollection#get}.
         * @param {String} id The component {@link Ext.Component#id id}
         * @return Ext.Component The Component, <code>undefined</code> if not found, or <code>null</code> if a
         * Class was found.
         */
        get : function(id){
            return this.all.get(id);
        },

        /**
         * Registers an item to be managed
         * @param {Mixed} item The item to register
         */
        register: function(item) {
            this.all.add(item);
        },

        /**
         * Unregisters a component by removing it from this manager
         * @param {Mixed} item The item to unregister
         */
        unregister: function(item) {
            this.all.remove(item);
        },

        /**
         * <p>Registers a new Component constructor, keyed by a new
         * {@link Ext.Component#xtype}.</p>
         * <p>Use this method (or its alias {@link Ext#reg Ext.reg}) to register new
         * subclasses of {@link Ext.Component} so that lazy instantiation may be used when specifying
         * child Components.
         * see {@link Ext.Container#items}</p>
         * @param {String} xtype The mnemonic string by which the Component class may be looked up.
         * @param {Constructor} cls The new Component class.
         */
        registerType : function(type, cls){
            this.types[type] = cls;
            cls[this.typeName] = type;
        },

        /**
         * Checks if a Component type is registered.
         * @param {Ext.Component} xtype The mnemonic string by which the Component class may be looked up
         * @return {Boolean} Whether the type is registered.
         */
        isRegistered : function(type){
            return this.types[type] !== undefined;
        },

        /**
         * Creates and returns an instance of whatever this manager manages, based on the supplied type and config object
         * @param {Object} config The config object
         * @param {String} defaultType If no type is discovered in the config object, we fall back to this type
         * @return {Mixed} The instance of whatever this manager is managing
         */
        create: function(config, defaultType) {
            var type        = config[this.typeName] || config.type || defaultType,
                Constructor = this.types[type];

            if (Constructor == undefined) {
                throw new Error(String.format("The '{0}' type has not been registered with this manager", type));
            }

            return new Constructor(config);
        },

        /**
         * Registers a function that will be called when a Component with the specified id is added to the manager. This will happen on instantiation.
         * @param {String} id The component {@link Ext.Component#id id}
         * @param {Function} fn The callback function
         * @param {Object} scope The scope (<code>this</code> reference) in which the callback is executed. Defaults to the Component.
         */
        onAvailable : function(id, fn, scope){
            var all = this.all;

            all.on("add", function(index, o){
                if (o.id == id) {
                    fn.call(scope || o, o);
                    all.un("add", fn, scope);
                }
            });
        }
    });