Specifying Branches?

[ms419]

How does one specify which branch is being checked in / out?

Please excuse me; I'm still learning : )

I wish to keep two "branches" of a file in RCS: "mine" & "dpkg". I've 
been over the man pages & gather this is possible, but the details are 
still a bit fuzzy: There doesn't seem to be a "--branch" flag, to 
specify which branch I'm checking in / out. I tried "ci -rdpkg.0 
nsswitch.conf", but RCS complained:

Symbolic name `dpkg' is undefined.

Can someone please clarify, how to maintain branches in RCS?

Thanks!

Jack