When cataloguing on a UNIMARC installation, clicking on the ? for field help now goes to https://www.ifla.org/, for example for 500: https://www.ifla.org/#500. This looks like a redirect from https://archive.ifla.org/#500 (the MarcFieldDocURL system preference indicates that http://archive.ifla.org is used if nothing is entered in the system preference).
I couldn't find the new location(s) for UNIMARC field help....if there is one.
It looks like the Italian version would work fine with MarcFieldDocURL, but most links, including to the English version are broken: https://www.ifla.org/publications/unimarc-formats-and-related-documentation/ Then there is https://www.ifla.org/g/unimarc-rg/unimarc-updates/, but it looks like the full documentation is not (or no longer?) available online. Maybe we should just remove the default URL for UNIMARC?
I also found: - https://www.ifla.org/g/unimarc-rg/unimarc-updates/ - https://www.iflastandards.info/unimarc (but it doesn't provide as good an explanation as the narrative information) Removing the default URL seems like a good plan!