Currently Mongoid configuration documentation, when it comes to the code needed to configure Mongoid (i.e. everything other than the listing of Mongoid configuration options), is a bit of a patchwork. This ticket proposes to rework the related documentation to clearly cover:

How to load Mongoid configuration in non-Rails context
That in Rails context Mongoid configuration does not need to be explicitly loaded
That Mongoid environment determination is only relevant when not running in a Rails context
How to load a hash of configuration options programmatically - this is not supported as far as I can see
That environment applies to hash of options loaded programmatically but not to options set in Ruby code