Perl 5.30.2 replaces some invalid UTF-8 byte sequences inconsistent with current best practices.

[flenniken]

Perl 5.30.2 replaces some invalid UTF-8 byte sequences inconsistent with current best practices.

The Unicode specification says:

An increasing number of implementations are adopting the handling of
ill-formed subsequences as specified in the W3C standard for encoding
to achieve consistent U+FFFD replacements.

See:

• Unicode 14.0 -- Unicode 14.0 Sp
  ecification -- Conformance page 126, section 3.9.
• w3.org Encoding -- w3.org encoding

For example, the hex byte sequence:

<e0 80 7f>

gets encoded as:

<ef bf bd 7f>

instead of:

<ef bf bd ef bf bd 7f>

Here are a few more examples:

Perl decode: e0 80 80
expected: ef bf bd ef bf bd ef bf bd
got: ef bf bd

Perl decode: f0 80 80 80
expected: ef bf bd ef bf bd ef bf bd ef bf bd
got: ef bf bd

Perl decode: ed ae 80 ed b0 80
expected: ef bf bd ef bf bd ef bf bd ef bf bd ef bf bd ef bf bd
got: ef bf bd ef bf bd

See https://github.com/flenniken/utf8tests for more information.