Dear Taco, I would like to add some additional fields to bibliography. I know that I have already asked the same question twice (for url and doi) and each time it has been built into the core functionality, while my current request is "too local" to do that. I would like to have \newbibfield[cobissid] \startpublication [...] ... \cobissid{70615} \stoppublication and then I would modify \setuppublicationlayout[book] to transform the number written above into "cobiss.si-id: 70615" pointing to the following URL: http://www.cobiss.si/scripts/cobiss?command=DISPLAY&base=cobib&rid=70615&lani=EN That is very similar to what DOI does at the moment, but while DOI is quite international, COBISS ID is really local, but it is *the* system used in the whole country. Is there any simple & safe way to achieve that? Thank you very much, Mojca