The source code

    /**
     * xtemplate runtime
     * @author yiminghe@gmail.com
     * @ignore
     */
    KISSY.add('xtemplate/runtime', function (S, XTemplateRuntime, commands, includeCommand) {

        /**
         * add command to all template
         * @method
         * @static
         * @param {String} commandName
         * @param {Function} fn
         * @member KISSY.XTemplate.Runtime
         */
        XTemplateRuntime.addCommand = function (commandName, fn) {
            commands[commandName] = fn;
        };

        /**
         * remove command from all template by name
         * @method
         * @static
         * @param {String} commandName
         * @member KISSY.XTemplate.Runtime
         */
        XTemplateRuntime.removeCommand = function (commandName) {
            delete commands[commandName];
        };

        XTemplateRuntime.commands = commands;

        XTemplateRuntime.includeCommand = includeCommand;

        var subTpls = {};

        XTemplateRuntime.subTpls = subTpls;

        /**
         * add sub template definition to all template
         * @method
         * @static
         * @param {String} tplName
         * @param {Function|String} def
         * @member KISSY.XTemplate.Runtime
         */
        XTemplateRuntime.addSubTpl = function (tplName, def) {
            subTpls[tplName] = def;
        };

        /**
         * remove sub template definition from all template by name
         * @method
         * @static
         * @param {String} tplName
         * @member KISSY.XTemplate.Runtime
         */
        XTemplateRuntime.removeSubTpl = function (tplName) {
            delete  subTpls[tplName];
        };

        // can only include compiled sub template
        XTemplateRuntime.IncludeEngine = XTemplateRuntime;

        return XTemplateRuntime;
    }, {
        requires: ['./runtime/base', './runtime/commands', './runtime/include-command']
    });

    /**
     * @ignore
     *
     * 2012-09-12 yiminghe@gmail.com
     *  - 参考 velocity, 扩充 ast
     *          - Expression/ConditionalOrExpression
     *          - EqualityExpression/RelationalExpression...
     *
     * 2012-09-11 yiminghe@gmail.com
     *  - 初步完成，添加 tc
     *
     * 对比 template
     *
     *  优势
     *      - 不会莫名其妙报错（with）
     *      - 更多出错信息，直接给出行号
     *      - 更容易扩展 command,sub-tpl
     *      - 支持子模板
     *      - 支持作用域链: ..\x ..\..\y
     *      - 内置 escapeHTML 支持
     *      - 支持预编译
     *      - 支持简单表达式 +-/%* ()
     *      - 支持简单比较 === !===
     *   劣势
     *      - 不支持表达式
     *      - 不支持复杂比较操作
     *      - 不支持 js 语法
     *
     */