Threads and forum channels
Branch a conversation off a message, or run a whole channel that way
A thread is a side conversation hanging off one message. It keeps a busy answer, or a long back-and-forth, out of the main channel while staying one click away from it.
Starting a thread
Hover a message in a channel and you'll find a reply-in-thread icon among the message actions. Click it to start a thread from that message. It opens a panel next to (or over) the channel, with the message you started from at the top.
You can't start a thread from a direct message, or from a message that's still sending or failed to send.
Replying
The thread panel has its own composer at the bottom, the same one the channel uses: attachments, mentions, the emoji picker and a typing indicator all work the same way inside a thread.
Once a message has a thread, the message itself grows a small button showing how many replies it has. Click it to open the thread. That count is just a size: it stays at "12 replies" whether or not you've read any of them, so it doesn't tell you what's new.
Unread and mentions
What's actually new shows up next to the reply count, as a badge separate from it: how many replies you haven't read, and how many of those named you. The same badge appears on a thread's row in a forum channel.
Being mentioned inside a thread also badges the channel it hangs off, the same way a mention in the channel itself does — you don't have to have the thread open to notice.
Marking a thread solved
Whoever started the thread, and any moderator, gets a Mark solved button in the panel's header. Marking it solved adds a "Solved" chip next to the reply count and title.
The same people can Reopen a solved or closed thread from that button. Everyone else can still read a solved thread and reply to it like any other; marking it solved doesn't lock it.
Closed threads
A closed thread has no composer. In its place, the panel just says the thread is closed and you can't reply to it. The starter or a moderator can reopen it from the header, same as a solved one.
Forum channels
A forum channel replaces the usual message list with a list of topics. Each topic is really a thread: starting one opens the same panel described above, with the first post as the root message.
A topic row shows its title, who started it, its reply and participant counts, when it was last active, and — where the channel has any — the tags attached to it. Solved and closed topics carry the same chips as a thread does.
Filter the list with the buttons across the top: All, Unanswered, Solved, Closed and Mine, each showing how many topics match. All leaves closed topics out of the count and the list, which is what the Closed filter is for — without it, there'd be no way back to something that got closed.
Starting a new topic asks for a title and a first post, and lets you pick from the channel's tags if it has any. Click a tag in the filter bar to narrow the list down to topics carrying it.
Where the panel sits
On a wide enough window, the thread panel sits beside the conversation as its own column, with the channel keeping the width it's drawn at. On a narrower window there isn't room for both, so the panel takes the whole pane instead, with a back arrow in its header to get back to the channel.