BOOL, can be read and set, but not unset.

Available infetch

Whether to process the backend response for Edge Side Includes (ESI) tags. The default value is false.

Setting this to true has the same effect as invoking the esi statement, except that the value of beresp.do_esi can be changed once set. (ESI processing is performed after vcl_deliver, so the value only takes effect at that point).