When offloading a hook implementation to another function, which function should be documented as "Implements..."? This is a (probably super simple) document standards-related question.

Example:

_menu_block_block_configure - DrupalContrib

Note the docs: "Implements hook_block_configure()."

It initially threw me off to see an internal function (with underscore prefix) documented as a hook implementation, but if the actual work is being done here then there is some sense to it. 

My question: is this the proper way to document it?
TL;DR: Yes, it's fine and widespread too!

It might look kinda unorthodox but it's just offloading the bulk of the hook implementation to an include to keep the main .module file smaller.  Here's where it's happening: menu_block.module (view source at the bottom).

A lot of other contribs do this too, for example: Display Suite (see line 48 onwards) and I'm pretty sure Views and a bunch of others too.