The discussion is about creating a feature to hide content from subsets of users using BBCode. Monikas proposed adding BBCode to hide content from non-logged in users, until a user likes the post, or until a user replies to the post. [Heliosurge](/t/-/303181/2, /t/-/303181/3) suggested adding an option to hide content from users not in a targeted group and noted that the “reply” feature might be less useful since users are taken away from the post after replying.
hello-smile6 questioned how this could be implemented server-side, and Heliosurge suggested a plugin would be needed. [nwnuyhs](/t/-/303181/6, /t/-/303181/10) expressed interest in the feature and proposed a “Hidden Content Feature” with visibility conditions such as visible after reply, login, or based on trust level.
Moin clarified that the current “hide details” and spoiler functions do not adequately address the request, as anyone can read the text. merefield and Moin shared similar requests from other discussions, including https://meta.discourse.org/t/show-spoiler-content-on-like/316229 and https://meta.discourse.org/t/group-specific-whispers-in-addition-to-staff/233114/23.
Overall, the feature request aims to provide a way to share content with specific groups of users, such as logged-in users or users who have replied to a post, without making the content publicly visible.
Developing a plugin allows users to hide content from other users by using BBCode.
[LOGIN]content to hide[/LOGIN] : hides the content from the non-logged in users[LIKE]content to hide[/LIKE] : hides the content until the user likes the post[REPLY]content to hide[/REPLY] : hides the content until the user replies to the postThe first too seem pretty cool. Though the last one typically once the reply is posted it jumps the user to their reply. So they might not see the hidden content that is revealed upon creating the reply.
I would add option to hide from users not the Op that are not in a targetted group.
This request is similar iirc was for a Tabletop RPGs forum
How could this even be implemented server-side, since anyone can see a post’s raw contents?
You would need a plugin I believe for server side
This looks like it should work but might need some fix ups
Need this feature
I not really clear on how the hide details or spoiler functions don’t do this adequately. 
Everyone can read text in “hide details” and spoilers. The request is to allow only logged-in users, or users who replied to or liked the post, to read this part of the post.
For example, you can share a discount code with your members in an announcement that everyone can read. At the moment, you would have to put the code into a different post in a different category.
Hidden Content Feature:
Use hidden code to conceal content, with the ability to set visibility conditions such as:
For example：
[hide] content [/hide]
I think Show Spoiler Content on 'Like' is also included in this request
This is a similar request:
This one might get be harder/less useful in part.
As once you reply your taken away from the post your replying to. So the user would need to venture back to the post in question.
I do see value though in the overall feature request. For things like table top RPG type forums you might want to send a hidden message to a player or game master. For that purpose a Customization > Theme component can work as long as it is clear not to use for security sensitive info. For that a plugin would be needed.