Well, I've just checked and it is not the actual package code.
I remember now that I found the example of custom ConsumerInterface in the documentation of XML::SAX::Writer 
    sub output {
        my $self = shift;
        $$self .= uc shift;
    }

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and I have adapted it to my needs: replacing the string scalar to store the data by a file handle. Thus I am responsible for print $$self $data;. Actually I was surprised for not having the warning while using the stock module... Mea culpa.

In reply to Re^4: "scalar found where operator expected" while printing to a glob ref by seki
in thread "scalar found where operator expected" while printing to a glob ref by seki

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