[Koha] About example with the 952 field

Hi All, In "Koha 3.14 Manual (en)" there is the "Tag 952 Subfield constraint" table (see section '4.1.4. Edit Framework Subfield' of the chapter '2. Administration'). Why exactly 952 ? Is it accident ? Maybe, this field randomly has been selected as an example of the ordinary field ? Or, maybe, this is more essential, the 952 field is a special field in the Koha system ? For instance, not for cataloging but for a management ctalogues. Regards, Gennady