This API aggregates top-level metrics associated with "recs" events; events for impressions and clicks delivered through /public/widget/data.
The API uses the same request, response and limitations as for /traffic, except that that the only fields that can be aggregated are events, uniqueUsers, and fraction where events is an implicit field.
events here is the number of times the URL was shown as a recommendation, while fraction is weighted by the number of results in a recommendation widget (counting 1/3 if the URL was one out of 3 URLs recommended in a single widget).