XML::Twig->new(
    twig_handlers => {
        span => sub { $_->replace_with($_->children_copy) },
    },
)->parse(<<'XML')->print;
<d>
  <span>
    foobar
    <span>
      <baz>bax</baz>
      <span style="color:#000000;">
        <ix:nonNumeric name="uk-bus:PrincipalLocation-CityOrTown">Lond
+on</ix:nonNumeric>
      </span>
    </span>
  </span>
</d>
XML

print "\n";

__END__
<d>
    foobar
    <baz>bax</baz><ix:nonNumeric name="uk-bus:PrincipalLocation-CityOr
+Town">London</ix:nonNumeric></d>
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