Wups - there's a bug in that version of _nsc. Here's a better one:

sub _nsc
{
    my @a = @{$_[0]};
    my @b = @{$_[1]};
    @a && @b or return( @a ? 1 : @b ? -1 : 0 );
    my $x = shift @a;
    my $y = shift @b;
    $x =~ /\d/ ? ( $y =~ /\d/ ? length($x)<=>length($y)
    || $x <=> $y || _nsc(\@a,\@b) : -1 ) : ( $y =~ /\d/
    ? 1 : lc($x) cmp lc($y) || _nsc(\@a,\@b) )
}
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(This version also optimizes to only compare numeric strings as numbers iff they have the same length.)