Another aspect to consider is that the developer bestk knows what
a new feature is about and how and in which musical context to use
it.
A doc writer, on thze other hand might not have any idea where the
feature can be used (because it is from an area where he is not
proficient) and how important it really is. So I would prefer it
if the
developer writes some raw documentation, which can then be
improved by a dedicated doc writer. That way, the dev ensures that
all important information about the feature is in the docs, while
the
doc writer ensures that users will understand it.