Out of bounds negative index

Hi,

 From the R Language Definition, Section 3.4.1:

 "If i is positive and exceeds length(x) then the corresponding selection is
NA. A negative out of bounds value for i causes an error."

 (This is also mentioned in S Programming, footnote of page 24.)

 Can someone please provide an example triggering the error? Looking in
src/main/subscript.c I could not find exception handling for |i| >
length(x), unless the negative subscript is mixed with NAs. In other cases,
out of bounds negative indexes just seem silently ignored.

 Did I missed or misinterpreted something, here?

a <- 1:10
a[NA]

a[-NA]