This works the same way as `substr`, but in addition allows negative indexing.
Negative indicies count backwards from the end of the string, with -1 being the last character.
x <- c("fa\xE7ile", "hello world")
Encoding(x) <- "latin1"x <- sf_iconv(x, "latin1", "UTF-8")
sf_substr(x, 4, -1) # extracts from the 4th character to the last## [1] "ile" "lo world"