mongodb/docs — pull request #59 by oliverlloyd (2012-07-10 22:49:46+00:00)
Title: Added an example for an aggregate key as this was not clear.

Grouping over multiple fields is a clear use case for many people but this is not shown in any examples here and the format required for the aggregate key is inconsistent (you do not specify $name but simply name) so adding an example would probably save a few people some frustration, esp. those not coming from a background of using the previous collection.group method.