Elasticsearch needs the ability to map the index according to the MARC field indicator. For example, the value of the 2nd indicator of field 264 defines whether it is a publisher, manufacturer or distributor. These operators should be able to map to different indexes.
Still valid. Needed also for UNIMARC, for the same use case
Same idea for Zebra : https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=12813
Maybe it could be useful for https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=33139 too