Thanks that's interesting, I'll have to try that. I'm going to add this to the post too did you have a link you want me to add?
-x attaches to a non-detached session aka multi-display mode, stereotypical pair programming / tutorial / support use.
-RR reattach and if necessary detach (overridden by -x above) or create it (as happens on first login after a reboot) and use youngest session if multiple sessions somehow accidentally get opened.