this would be a great addition, i am surprised we are only now facing an issue where we need this, but now that we do we are facing quite the struggle that we can't do it with firebase natively

When querying a document attribute which is an array of strings, such as tags or labels associated with a document, it can become necessary to say that 'at least the queried strings' are present in the array.

For example consider the following entities:

London: {labels:["south", "england", "cold"]}
Manchester: {labels:["north", "england", "cold"]}
New York: {labels:["east", "usa", "cold"]}
California: {labels:["west", "usa", "warm"]}
Texas: {labels:["south", "usa", "warm"]}

To retrieve all documents with tags/labels including both 'cold' and 'england' (London, Manchester) an array-contains-all operation should be used.

'array-contains-any' would return [London, Manchester, New York].
'in'/'array-contains-only' would return no results (query length does not match).

Proposed 'array-contains-all' would correctly return [London, Manchester].

'array-contains-all' can of course be accomplished by post-filtering array-contains-any results, however if there are a large number of entities then this becomes a very inefficient solution with respect both to the database query response time/payload size and the post-processing time.

Individual boolean attributes could be assigned for each label, this is however unfeasible when a very large/growing number of (possibly user-defined) unique tags/labels are possible.

We have a very large number of documents with hundreds of unique labels being used to filter and serve content in response to user actions with a requirement for very low-latency.
array-contains-any is a very inefficient approach to retrieve those few documents containing all the labels queried/requested.
We need the array-contains-all operator.

need to define if this is different from a 'array-contains-only' situation

isn't this an 'in' operator?

Two use cases: 1) Docs with array of tags, pull back only documents with tags X and Y. 2) Docs representing conversations with array of participant user IDs, pull back only conversations that include both participants A and B.

This is very much needed, I don't understand why we don't already have this. We already have array-contains and array-contains-any, it only makes sense to add array-contains-all.