Ran the MARC bibliographic framework test on a site with 11 frameworks and the test returned all OK except for one. I received an error for the biblio and biblionumber test with: "The biblio.biblionumber and biblioitems.biblioitemnumber fields be mapped to a MARC subfield," I interpreted this to mean the 999$c and 999$d are not mapped. But the Koha to MARC mapping does show the fields are mapped. Checking the frameworks, the 999$c and 999$d are set to ignore. I have checked other sites where this error does not appear and the 999$c and 999$d are configured exactly the same. Some additional clarity or explanation is needed to understand this message. It does not appear the message is actually referring to the 999$c or 999$d, but something else. Because the message is non-specific and providing an incorrect reference, it is very difficult to comb through each framework, tag, and subfield to find the actual error. The error message also does not seem to be an obvious blocker. There are sites operating, without apparent data problems, with this error. Related to bug 18576
Document the error messages in the manual. There is currently next to nothing in that section https://koha-community.org/manual/latest/en/html/administration.html#marc-bibliographic-framework-test
Note to not forget: Esther's problem ended up being that one of the frameworks had the 999$c and 999$d in tab 0 instead of -1. But the message was The biblio.biblionumber and biblioitems.biblioitemnumber fields be mapped to a MARC subfield. Whoever does the docs will need to add that as a potential solution for that error message.