Cross Reference Options

1) On the website, I can cross reference a collection with a tag, but on the app, I cannot. Is this something that could be added as a mobile feature?
2) It would be great to be able to cross reference multiple tags and/or multiple collections. If it’s possible, it would be nice to be able to do that on the website (if not also the app).

What do you mean with cross-reference multiple collections/tags?

Show books that are in both collections/tags? Or something else?

And what do you mean with "cross reference a collection with a tag"?