[Yum] simple newbie-level questions/clarifications

[Robert P. J. Day]

  (the first in what will undoubtedly be many questions in order to help
me write my doc.)

  is there any way (or rationale) to distinguish between repositories
listed in /etc/yum.conf?  let me explain.

  if, as a regular user, i run "yum list", this will (AFAICT) list for me
all packages available from *all* listed repositories in my /etc/yum.conf
("available" appearing to mean all packages that are either newer than
installed packages or are packages not installed at all on my system,
right?)

  can i restrict my list to just those from a selected subset of those
repositories?  i may have different repositories for different reasons.
one repository could, for instance, be strictly for multimedia apps.
or i could pick on, say, matthias' freshrpms repository just to see
what's new(er) there.  can i restrict my output of "yum list" in that way?
it doesn't seem so from the man page, but perhaps i missed something.

  and this might be related to the "group" feature of yum of which i
have no idea, and which is not documented in the man page.

rday