Can't observer 'checkout_submit_before' event in frontend event area.

[hostep]

Preconditions

1. Magento CE 2.1.2
2. PHP 7.0.12
3. A store with some products and a way to create orders on the frontend

Steps to reproduce

1. Create a new working module
2. Add a file: etc/frontend/events.xml and etc/events.xml file
3. In both files add an observer for the event checkout_submit_before (make sure they have a different name) and make it call a method which outputs something in a log file to see which of the two observers was called.
4. Flush your caches
5. Go to the frontend and place an order

Expected result

1. There should be 2 entries in the logfile, one for the 'global' observer and one for the 'frontend' observer

Actual result

1. There is only 1 entry in the logfile, the one for the 'global' observer, the one for the 'frontend' observer is missing

Discussion

I think this is a bug, but I'm not sure. If this is expected behavior I would have expected to find some documentation where this is being explained.

[hostep]

Of course, 5 minutes after creating this issue, I find this other issue which explains why it doesn't work: #1581
And after testing, it actually works like explained over there.

So this is clearly a documentation issue, because this webapi_rest event area is not mentioned in the docs currently...

Closing this issue, I'm going to open one over at the devdocs repo.