Merge branch '6590-api-config-docs'

I am breaking our own rules here, since this merge includes a
non-trivial commit from me that hasn't been reviewed.  I'm going ahead
with it because I understand the driving motivation of branch reviews
is to make sure two sets of eyes see changes that could impact future
work, and I think that's been accomplished here.  My changes only
touch what Peter had already changed.

Plus, with Peter out for a week, the benefits of merging outweigh the
value of holding back.  Users get the benefit of improved
documentation immediately; we'll look better at sprint review; and
documentation mistakes are comparatively easy to fix after the fact.

Closes #6590, #6721.