I'd need to (laboriously) check the source for chapter and verse, but as far as I remember in all the obvious cases when any of the inputs have UTF8 on, the output will too.

Here's an example commonly used in perl's tests to create a UTF8-flagged string by appending a flagged zero-length string:

% perl -MDevel::Peek -wle '
  $x="\x{100}"; Dump($x);
  chop $x;      Dump($x);
  $y = "foo";   Dump($y);
  $y .= $x;     Dump($y)
' 2>&1 | grep FLAGS
  FLAGS = (POK,IsCOW,pPOK,UTF8)
  FLAGS = (POK,pPOK,UTF8)
  FLAGS = (POK,IsCOW,pPOK)
  FLAGS = (POK,pPOK,UTF8)
%

[download]

Your examples certainly all appear to propagate the flag. However substr() appears to propagate it only if the resulting substring source string has characters above 0x7f: I have no idea why that appears to be an exception. And I also do not know of any guarantee that any of these behaviours will be retained in future perl versions (though I think it is hugely unlikely that the steps involved in the code above will change, due to its widespread use in core).

Update: from perl source, it appears substr returns a UTF8_off result if the source string has byte length and character length the same.

In reply to Re^5: Seeking Perl docs about how UTF8 flag propagates by hv
in thread Seeking Perl docs about how UTF8 flag propagates by raygun

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