An aggregate query with multi-level grouping is returned as a nested document. When the TOP, BOTTOM, FIRST, or LAST functions are used, the limit value is normally applied to the corresponding grouping level only. For example:This query returns the first 10 Sender.Person.LastName groups, but it returns all FirstName subgroups for each LastName group. The query can be flattened by adding the REST parameter &flat=true:This returns only the top 10 LastName/FirstName group pairs. This allows a more predictable result size, e.g., when the results will be displayed in a web page.