[texhax] derivatives and integrals: math operators

[Natércia Fernandes]

Hi.
Math operators should be typeset in upright letters and also have a special 
spacing.
So shouldn't the "d" of derivatives (or integrals) be set with upright 
letters, since both are mathematical operators?

Already in 1997, there was an article published in TUGboat (Typesetting 
mathematics for science and technology according to ISO 31/XI) by Claudio 
Beccari and available at 
http://www.tug.org/TUGboat/Articles/tb18-1/tb54becc.pdf where he says that the 
"d" of derivatives and integrals should be upright (see item number 6).
It seems to make sense and I've been using it.

But at the same time, I haven't seen it being followed by other people...  For 
example, the work of Lars Madsen Introduktion til LaTeX doesn't.

Can anyone clarify this point to me, please?

Thank you very much,
Natércia