Thank you, Andrew! As you suggested, I fixed the missing fields = ‘__all__’ in several places (requirement for explicit fields = ‘__all__’ is relatively new — it is enforced by DRF 3.4+).
As for display of nested fields in Browsable API — I didn’t make them properly display in HTML tab yet.
Unfortunately, the logic of form inputs generation for serializer fields is hard-coded in DRF’s https://github.com/tomchristie/django-rest-framework/blob/master/rest_framework/renderers.py in a single place for all fields. I think, I can do something about this - override this `HTMLFormRenderer`- if I wanted nested fields to be properly displayed in the Browsable API HTML tab. Just didn’t have enough time to do this yet.
Currently, I’m mostly using Raw data tab.