mongo node driver object reference

In order to write an app handling the database responses I need to know the possible structures and values of the ubiquitous error parameter.

all the callbacks have:

function(err, res) ...

Does anyone know about the structure of the err object?

When provided to the callback, the err parameter contains an Error-based object. The name property of the object can be used to differentiate the types of errors, and the message property contains a string description of the error.

Looks like $err is usually a string type. See http://jp.wiki.mongodb.org/display/DOCS/Error+Handling+in+Mongo+Drivers