Yes, I got the various ways of attaching info to such objects (confession: $$self->{'xyz'} = 42 is what I would seek first - and I should have realised myself) thanks to the respondents to this question. It's just I sense that maybe is not a "good" thing to do, given that the author did not make it explicit/easy to subclass for users.

Btw, from Furl's source I see in new()

...    
return bless \(Furl::HTTP->new(header_format => Furl::HTTP::HEADERS_AS
+_HASHREF(), @_)), $class;
[download]

And now I wonder whether this "special" blessing which has been tormenting me was just because of not wanting to explicitly subclass.