Using Weight Window Generator

Dear OpenMC Forum,

I’m trying to use the Weight Windows with MAGIC, following the information in Section 17.1 of the User’s Guide. Referring to the example code therein reported, I do not find any reference to the specific tally that the Weight Windows’ generator is supposed to use as flux reference. Is it implied that is uses a (single?) tally or mesh-tally previously defined and run? Is there a way to specify a reference tally or mesh-tally?

Thanks in advance

Gabriele