Facebook is experimenting with privacy settings that apply to individual comments. This means that you could write a reply to a thread, but only pre-approved individuals can see it. Here’s what it looks like:
Clicking the padlock icon brings up the security settings. This has four options: friends and post owner only; friends only; post owner and commenter only; and everyone else.
From what we can tell, this is a small-scale test that’s only available to a handful of users. That’s a shame, because I can imagine this being beneficial for engagement.
On a hotly contentious news story, for example, someone may be wary of posting a comment, lest they receive abuse. By ensuring the comment is only viewable by their friends, this isn’t an issue.
We’ve reached out to Facebook for comment, and to ask about plans for a wider roll-out. If they get back to us, we’ll update this piece.