Newbie trying to understand $ so I can understand acf function in stats

I am trying to understand the function acf
stats:::acf shows me the function

I am having trouble understanding the usage "$acf" in the following

   acf <- array(.C(R_acf, as.double(x), as.integer(sampleT),
         as.integer(nser), as.integer(lag.max), as.integer(type ==
             "correlation"), acf = double((lag.max + 1L) * nser *
             nser), NAOK = TRUE)$acf, c(lag.max + 1L, nser, nser))

I interpret it as ... we are forming an array of dimensionality 3, and 
the contents of the array come from invoking a C program R_acf while the 
values of the 3 dimensions are lag.max + 1L, nser, and nser.

simplified acf<-array(.C(args)$acf, c(some dimensions))

Adding some spaces and line feeds to make it easier to read
    acf <- array
(
   .C(
     R_acf,
     as.double(x),
     as.integer(sampleT),
     as.integer(nser),
     as.integer(lag.max),
     as.integer(type == "correlation"),
     acf = double((lag.max + 1L) * nser * nser),
     NAOK = TRUE
     )$acf,

   c(lag.max + 1L, nser, nser)
)

R Language Definition section 3.4 "Indexing" explains that $ is used in 
indexing.
But
The light is not coming on when I try to apply that knowledge to 
understanding what is happening here.

Can anyone suggest a path out of the darkness?

Also, when I search my system for a file named R_acf, I dont find one.
I assume that this is because R_acf got task built into an executable 
and my distribution has the executable? I got R from "yum install R" on 
fedora linux. To see the source I apparently need to download a full 
compilable distribution of R.

Dick