Thread Types Plus adds a new feature to XenForo: Post comments. By default, Post Comments are enabled for all thread types, but this can be limited with a number of options. To limit post comments, navigate to ACP > Setup > Options > [TH] Thread Types Plus: Post comments, to find the following options:
Enable post comments on first post allows you to regulate which thread types support commenting on the first post of each thread. As creating a normal post within the thread is effectively a comment on the first post, this option allows you to turn commenting off specifically for this post.
Enable post comments on replies in turn allows you to regulate which threads support commenting on all posts except the first post.
Post comments are functionally handled equivalent to Profile post comments. Commenting on a post will alert the post author as well as all other users that have left a comment on the same post. Users can disable these alerts in their preferences under Receive a notification when someone… Comments on your thread, Comments on your post and Also comments on a post.
As posts, Post comments support reactions, votes, reporting, moderation queue, and are fully searchable. Their default sort order can be configured under ACP > Setup > Options > [TH] Thread Types Plus: Post comments > Post comment sort order.