http://erlang.org/eep/eeps/eep-0048.html

The goal is to introduce Code.fetch_docs/1 that returns the format in the EEP (or {:error, _} if the chunk is not available). Since the old documentation chunk will no longer exist, Code.get_docs/2 should be changed to always return nil - which is a backwards compatible result - and be scheduled for deprecation.

We will also use the new chunk metadata to store relevant information, such as "defaults", "deprecated" and "since".

Replaces #3589.