[phenixbb] Meaning of "resolution" keyword for phenix.real_space_refine with mrc/ccp4 map input?

Hi, What exactly does phenix.real_space_refine do with the mandatory "resolution=" keyword when refining a model against a ccp4/mrc formatted map? Is this purely for adjusting restraints etc, or does phenix internally low-pass filter or resample the map based on this parameter? This seems like a basic question, so I apologize if the answer is staring me in the face, but I couldn't see it in the online documentation or in the output of phenix.real_space_refine --help. Cheers Oliver.