code: function Spec(cidKey, sidKey) {
      if (!_.isString(cidKey))
          throw new TypeError("cid should be a string, such as 'genBasic'.");
  
      if (!_.isString(sidKey))
          throw new TypeError("sid should be a string, such as 'attrs' and 'cmds'.");
  
      this.cid = cidKey;    // cid is a string
      this.sid = sidKey;    // sid is a string
  }
docs: sid: [ 'dir', 'attrs', 'acls', 'cmds', 'cmdRsps' ]