Callbacks: v2_runner_on_ok vs v2_playbook_item_on_ok?

Hello.

I need to get some feedback from ansible runs. I use custom callbacks for this task.
Could someone describe difference between v2_runner_on_ok vs v2_playbook_item_on_ok methods?

During my test runs I see that the v2_runner_on_ok is called when tasks are done, but when is v2_playbook_item_on_ok expected to be called?

Thanks!

v2_playbook_item_on_ok is not called 'yet', it is there as placeholder
for when we reintroduce returning info per item, currently in 2.0 we
return all info at the end of the loop, which is not optimal (there
are open tickets on this issue).