That of the publisher

The Other Side of the Argument
As with anything , there are two sides to this argument. That of the publisher. And that of the reader
https://www.christopherfielden.com/short-story-tips-and-writing-advice/exclamation-marks.php

https://www.christopherfielden.com/short-story-tips-and-writing-advice/exclamation-marks.php
Please explain the grammatical form and function of "that" in " that of the publisher and that of the reader ".