Operations
The following high-level operations are described here after:
- FOR: Iterate over all elements of an array.
 - RETURN: Produce the result of a query.
 - FILTER: Restrict the results to elements that match arbitrary logical conditions.
 - SORT: Force a sort of the array of already produced intermediate results.
 - LIMIT: Reduce the number of elements in the result to at most the specified number, optionally skip elements (pagination).
 - LET: Assign an arbitrary value to a variable.
 - COLLECT: Group an array by one or multiple group criteria. Can also count and aggregate.
 - REMOVE: Remove documents from a collection.
 - UPDATE: Partially update documents in a collection.
 - REPLACE: Completely replace documents in a collection.
 - INSERT: Insert new documents into a collection.
 - UPSERT: Update/replace an existing document, or create it in the case it does not exist.
 - WITH: Specify collections used in a query (at query begin only).