My plan is to use the best and fastest YAML module for YAML load and dump in core (as Cpanel::JSON::XS for json).
But LibYAML is too strict for the CPAN::Meta validation tests.
The root cause is that CPAN::Meta::YAML is broken, accepting too much illegal YAML.
I cannot load too many .yml files from CPAN prefs and build dirs.
So I am writing a NonStrict mode to workaround those quirks.

I'm ok with rejecting illegal structures, which would lead to
t/data-fixable/98042513-META.yml being not fixable but illegal.

    Class::Date:                   ^A^A^F

because the value for Class::Date is missing, and will not be assigned to undef (as CPAN::Meta::YAML, i.e. YAML::Tiny) does.

But this should be fixable with my new $NonStrict flag:

    Class::Date:                   0^A^A^F

The illegal control characters are ignored then.

$ cperl -MYAML::XS -e'$YAML::XS::NonStrict=0;$h=YAML::XS::LoadFile("t/data-fixable/98042513-META.yml"); print %$h'
YAML::XS::LoadFile Error: The problem

    control characters are not allowed

was found at document: 29, offset: 395
$ cperl -MYAML::XS -e'$YAML::XS::NonStrict=1;$h=YAML::XS::LoadFile("t/data-fixable/98042513-META.yml"); print %$h'
... (nyi)

The 2nd problem is an illegal utf8 codepoint conflicts with perl core.
There I'm not sure yet if its a libyaml bug or a CPAN::Meta bug or really an illegal utf8 codepoint:

YAML::XS::LoadFile Error: The problem

invalid trailing UTF-8 octet

was found at document: 25708, offset: 70

not ok 40 - t/data-test/unicode.yml validates
#   Failed test 't/data-test/unicode.yml validates'
#   at t/validator.t line 40.
# ERRORS:
# Missing mandatory field, 'version' (version) [Validation: 1.0]

Ok with this plan?

BTW: As you can see in the errmsgs I have already written a XS version for LoadFile,
which uses the better file iterator. Unfortunately I haven't yet wired the filename from XS down to libyaml, which only needs a FILE*. So the errmsg is not good enough yet. But still better than now. You'll see with my upcoming PR.