Yes, I too have encountered this in the process of working on issue 14626. For this purpose it is appropriate to use a special converter (with 'O&'). I suppose it must be a strict сonverter; there is no point in specifying followlinks=[1, 2, 3]. If it is somewhere need a nonstrict ones -- use 'O' and then check the how to in this particular case.

Would be good to have a special letter for this format, but note that 'b' and 'B' are already used. It is better first to use the сonverter, and expand the format only when the enough number of uses.