So what the selection of videos cover, the principle is straight forward enough, but there isn’t any collection data to query or code to look at while the video is running, without having to type it all in yourself.
Without any collection data to query, it makes it hard to work out, how the actual data is embedded within the resulting documents. Watching the video, doesn’t really show the all_reports, and how the data is stacked. Is it all flat, or is it embedded within itself, as you flow down the direct_reports.
In the end I went to the documentation and looked at the examples it gave.
EDIT: So I see that the cross Collection Lookup appears to use the air_airlines collection.