GENE basic overview is described here, I'll describe more advanced stuff here.
GENE is able to do automatic conversion of one exporter result type to another exporter source type, to a degree. This table summarizes possible conversions, with one exception: Object result is not convertible to anything but Object source.
When an exporter produces documents with multiple namespaces (DOM/SAX result type only) then the root
nametree is transformed and given to coordinator's partialResultEvent()
method before
a child nametrees are transformed.