logical, if TRUE then the function will not fail
but report success/failure via its result, otherwise failures are
considered errors.
charlen
logical, if TRUE then the function returns the
length of the longest byte sequence representing a character in the
file.
min.char
integer, any bytes below this value are considered
control chacters and reported as errors. The default value of 1L
guards against strings including NULs.
Value
If charlen=FALSE: TRUE on success, FALSE if the
payload is invalid and quite=TRUE.
If charlen=TRUE: positive integer corresponding to the
longest encoded sequence on success, negative integer on failure.