[Alpine-info] saving index/printing to file?

[Matt Ackeret via Alpine-info]

I see that if I turn this on:
      [X]  Print Index Enabled                                                   

then I can use the % print command from the INDEX screen.. and I see I can even set up multiple printers, even a custom command..

but I don't see quite exactly how to do what I want:

What I'd really like it to be able to save my current INDEX screen (e.g. selected messages) to a file..
if it's some randomly generated filename in /tmp, fine..

just so I can get a specific list of messages in a file that I can then do some
other things on them (e.g. pipe to some cut commands then sort then unique) 
to figure out some specific things from subjects of messages I save.

Can someone explain how to do that, get print to go to some filename, even if
it's the SAME filename always (but preferably not)?

thanks.