The description of the ElasticsearchCrossFields is technical correct, but for someone configuring Koha, it's not clear what the settings mean for using Koha. What's the consequence of choosing one setting or the other? It's only clear that you will need to use a specific Elasticsearch version.
It has a link to documentation that's not a link too :) https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-multi-match-query.html#type-cross-fields
In Koha, a 'keyword' search does not search a cpombined 'keyword' field, but rather searches your term across all the fields marked as 'searchable' in the current interface. Cross fields is used to determine whether you want to only return values where all entered terms are included in a single search field, or whether you wish to find a record with all terms, but allowing the terms to be in any combination of fields. e.g. "king grass" without cross fields will return: The Island of the Grass King by Nancy Willard (grass in title/king in title) with cross fields will return: The Island of the Grass King by Nancy Willard (grass in title/king in title) In the tall grass by Stephen King (grass in title/king in author)
I have just had a problem of a client disabling this (not sure why) and then their searches weren't returning the results they expected. I liked the description here https://bywatersolutions.com/education/elastic-search-configuration "More specifically, on Elastic 6 and later, if ElasticsearchCrossFields is turned off, Koha will look for all of your search terms in all of your search indices, but only return titles where all of your terms were in the same index. So a search for "bram stoker dracula" would not find the novel (as "bram stoker" is in the author and "dracula" is in the title), but might find you the 1992 film titled Bram Stoker's Dracula." For now, I added more info in the manual. Nick, I hope it's OK with you that I reused your example. https://gitlab.com/koha-community/koha-manual/-/merge_requests/733
(In reply to Caroline Cyr La Rose from comment #3) > For now, I added more info in the manual. Nick, I hope it's OK with you that > I reused your example. > https://gitlab.com/koha-community/koha-manual/-/merge_requests/733 Of course! Thank you!