So, that explains it. Thank you. I worked around the XML::Dumper issue with the following code:

my %tmp_h;
for (keys(%h)) {
    $tmp_h{$_} = {};
    %{$tmp_h{$_}} = %{$h{$_}};
}
pl2xml(\%tmp_h, 'h.xml');
%tmp_h = ();
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Where can I read more about LV scalars?