[R] What does m$... mean?

[Richard A. O'Keefe]

While reading through some of the R source code, I have come
across forms such as
    m$...
    m$... <- e
and I wondered what they meant.

?"$" mentions x$name, but not $... 
All it says is

     The operators `$' and `$<-' do not evaluate their second argument.
      It is translated to a string and that string is used to locate
     the correct component of the first argument.

Does this mean that m$... is the same as m$"..."
and m$... <- e is the same as m$"..." <- e?

That's what it seems to do when I try it on some small data frames,
but is that ALL there is to it, or is there some special magic going
on?  Is there any connection with the use of ... in formal and actual
parameter lists, or is it just accidental?  Why would anyone _want_
to use $... ?