Negative answer means that a string is surely not valid UTF-8.
Positive result does not mean that we should be absolutely sure.
E.g. (c4,85)
properly
represents ("Polish a with ogonek") in UTF-8
as well as ("A umlaut", "Ellipsis") in WINDOWS-1250.
Also note that UTF-8, as well as most 8-bit encodings,
have ASCII as their subsets
(note that stri_enc_isascii
=> stri_enc_isutf8
).
However, the longer the sequence,
the bigger the possibility that the result
is indeed in UTF-8 -- this is because not all sequences of bytes
are valid UTF-8.
This function is independent of the way R marks encodings in
character strings (see Encoding and stringi-encoding).