hook_views_post_render provides inaccurate information

Problem/Motivation

Original report:

The documentation at http://api.drupal.org says the following about this function's parameters:
string $output: A flat string with the the rendered output of the view.

This is incorrect. $output is a nested array of arrays and classes. If there's some string therein that can be manipulated, I haven't found it.

Additional things to consider:

#11:
Seems like this doc comment hasn't been updated since D7, and now I have no idea where to manipulate the rendered output.

#12:

I think more important is indeed to describe here that you should use the usual render API functionality to change the output, like #post_render.

#21:

During a views autocomplete, $output not a render array, it's an array of render arrays

Proposed resolution

1) Update the description of $output variable;
2) Get rid of legacy documentation that was relevant for D7 version and describe what can be done in this hook;

Remaining tasks

Review and commit.