Hi folks. My reading of the docs for decode function in the Encode module suggests that the utf8 flag on the resulting string should be off if the input string was plain ASCII. i.e. I'd expect the following: 
#!/usr/bin/perl
use warnings;
use strict;
use Encode;;

my $octets = "abcd";

my $ustr = Encode::decode('utf8', $octets);

print Encode::is_utf8($ustr)
      ? "is" : "isn't",
      " tagged as a unicode string\n";

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to print "isn't tagged as a unicode string".

But I don't, I get "is tagged as a unicode string" as the output.

What I believe to be the relevant section of the docs is: 

Here is how Encode takes care of the utf8 flag.

    * When you encode, the resulting utf8 flag is always off.
    * When you decode, the resulting utf8 flag is on unless you can
      unambiguously represent data. Here is the definition of
      dis-ambiguity.

      After $utf8 = decode('foo', $octet);,

        When $octet is...   The utf8 flag in $utf8 is
        ---------------------------------------------
        In ASCII only (or EBCDIC only)            OFF
        In ISO-8859-1                              ON
        In any other Encoding                      ON
        ---------------------------------------------

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I'm sure I've seen this not-tagging-ASCII behaviour in older versions of Encode (I think 2.01), too.

I'm running perl 5.8.8, Encode 2.12.

Can anyone else confirm that this is a bug, or have I got my encodings and flags in a twist.

In reply to Behaviour of Encode::decode_utf8 on ASCII by jbert

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