Extend search API to include a file's tag

I had built an Advanced Search application for Nextcloud, in order to enable some very specific file searching that can be quite useful (see some of the examples). I am undergoing a major overhaul to improve the performance of this application and have it show in the search bar instead of in a custom file table. I will then apply to provide it on the App Store.

One aspect of the Advanced Search application is the ability to limit the search to only a file's title or tag. Currently the Full Text Search API enables specifying a search in filename, but cannot specify a file's tag.

Is it feasible to extend the Full Text Search's API to include specifying the tag? That would then make it much easier to layer the Advanced Search application on top of it.

Start with the Full Text Search API documentation linked in the issue and compare its existing filename-search option with the Advanced Search application's tag-search need. Determine the API shape and scope required to filter by a file's tag; done means clients can request tag-limited searches and the behavior is documented and usable by Advanced Search.