    /**
     * @author Ed Spencer
     *
     * Proxy which uses HTML5 session storage as its data storage/retrieval mechanism. If this proxy is used in a browser
     * where session storage is not supported, the constructor will throw an error. A session storage proxy requires a
     * unique ID which is used as a key in which all record data are stored in the session storage object.
     *
     * It's important to supply this unique ID as it cannot be reliably determined otherwise. If no id is provided but the
     * attached store has a storeId, the storeId will be used. If neither option is presented the proxy will throw an error.
     *
     * Proxies are almost always used with a {@link Ext.data.Store store}:
     *
     *     new Ext.data.Store({
     *         proxy: {
     *             type: 'sessionstorage',
     *             id  : 'myProxyKey'
     *         }
     *     });
     *
     * Alternatively you can instantiate the Proxy directly:
     *
     *     new Ext.data.proxy.SessionStorage({
     *         id  : 'myOtherProxyKey'
     *     });
     *
     * Note that session storage is different to local storage (see {@link Ext.data.proxy.LocalStorage}) - if a browser
     * session is ended (e.g. by closing the browser) then all data in a SessionStorageProxy are lost. Browser restarts
     * don't affect the {@link Ext.data.proxy.LocalStorage} - the data are preserved.
     */
    Ext.define('Ext.data.proxy.SessionStorage', {
        extend: 'Ext.data.proxy.WebStorage',
        alias: 'proxy.sessionstorage',
        alternateClassName: 'Ext.data.SessionStorageProxy',

        //inherit docs
        getStorageObject: function() {
            return window.sessionStorage;
        }
    });