Hi, In Koha 3.20 it is not possible edit subfield $t of any field in the MARC framework. When for example accessing the "Tag 100 subfield constraints" a click on "Advanced options" will not open these options but CLOSE the "Basic constraints". It seems for subfield $t there is no way to open the "Advanced constraints" to edit visibility or anything else within these options. I guess this is not the way it should be. However, it is possible to get rid of the subfield $t by choosing "Managed in tab: ignore" in the "Basic constraints". This goes for all the MARC fields 100, 110, 130, 505, 600, 611, 630, 696, 700, 710, 711, 730, 796, 798, 798, 799, 800, 810, 811, 830, 856, 896, 897, 898, 899 and probably all MARC fields with a subfield $t. Can anyone give a hint or should I open a bug report? Best regards, Michael