how to use --pid-recursive

[Mark Croft]

i can't find any documention on  --pid-recursive

i am trying to download the complete series so far of "The Disappearance" BBC4

http://www.bbc.co.uk/iplayer/group/b05rcz9v

what i am doing wrong?

tried this nothing
 get_iplayer --subtitles --pid-recursive b05rd3lm

 get_iplayer --subtitles --pid-recursive --pid b05rd3lm
only gets first ep.

thank you