I am with you @jdfreder here, register all the transformers available in the Exporter base, and then we select which ones enable for each specific exporter... I think it is a better approach than register the some default transformers in each exporter to enable some of them later... In the current way, we are repeating ourselves (I mean duplicating code) and it is confusing for the people which do not know the internals of nbconvert.