Thanks, everybody.

It came down to some gradual, one-step-at-a-time debugging combined with your advice above.

The wrong code which caused the problem: 

    my $xhtml = HTML::TreeBuilder::XPath->new;
    $xhtml->implicit_tags(1);
    $xhtml->parse_file($file)
        or die("Could not parse '$file' : $!\n");

[download]

The code which prevented the mutilation of the data: 

    . . .
    use open qw/:std :utf8/;
    . . .

    my $xhtml = HTML::TreeBuilder::XPath->new;
    $xhtml->implicit_tags(1);
    my $filehandle;
    open ($filehandle, "<", $file)
        or die("Could not open file '$file' : error: $!\n");
    $xhtml->parse_file($filehandle)
        or die("Could not parse file handle for '$file' : $!\n");

[download]

So if I guess right, the use of a file handle which I have opened myself under the influence of the use open qw/:std :utf8/; pragma forced the data going into HTML::TreeBuilder::XPath to be read as UTF-8?

In reply to Re^3: Difficulty with UTF-8 and file contents by mldvx4
in thread Difficulty with UTF-8 and file contents by mldvx4

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