mmm, the use might be for package authors who want to re-define operators for certain classes (but that's not really exposed here, and is probably beyond the scope of the document then).

e.g. 

    "+.foo" <- function(x, y) sum(x, y) 
    x <- c(1, 2, 3) 
    y <- c(4, 5, 6) 
    class(x) <- "foo" 
    x + y ##21

this is used in e.g. ggplot2 to redefine `+` for adding layers and stuff, as an example.

there should probably be a section on `read.table` and all the surprising ways R can silently do things wrong