Add @+channel-context

client-tags/channel-context.md

@@ -0,0 +1,60 @@
+---
+title: "`channel-context` client tag"
+layout: spec
+work-in-progress: true
+copyrights:
+  -
+    name: "delthas"
+    period: 2022
+    email: "delthas@dille.cc"
+---
+
+## Notes for implementing work-in-progress version
+
+This is a work-in-progress specification.
+
+Software implementing this work-in-progress specification MUST NOT use the
+unprefixed `+channel-context` tag name. Instead, implementations SHOULD use the
+`+draft/channel-context` tag name to be interoperable with other software
+implementing a compatible work-in-progress version.
+
+The final version of the specification will use an unprefixed tag name.
+
+## Introduction
+
+This specification defines a client-only message tag to indicate the channel a private PRIVMSG or NOTICE should be displayed in.
+
+## Motivation
+
+Responding to PRIVMSG messages in channels with NOTICE messages in private is a widely-used IRC practice for bots, in order to prevent flooding a channel with messages only useful for a single user. Clients have developed heuristics for matching incoming private NOTICE to their channel context, but these heuristics are error-prone and difficult to implement for past messages with CHATHISTORY.
+
+This tag enables clients to systematically know in which channel a private PRIVMSG or NOTICE should be displayed, because the sender can now communicate that information in the message.
+
+## Architecture
+
+### Dependencies
+
+Clients wishing to use this tag MUST negotiate the [`message-tags`](../extensions/message-tags.html) capability with the server.
+
+### Format
+
+The channel-context tag is sent by a client with the client-only prefix `+`. The value MUST be a valid channel name.
+
+    +draft/channel-context=<channel>
+
+This tag MUST be attached to PRIVMSG and NOTICE messages to users only. Clients MUST ignore this tag if it is not attached to a private PRIVMSG or NOTICE message or if its value is not a valid channel name.
+
+## Client implementation considerations
+
+This section is non-normative.
+
+When clients receive a private PRIVMSG or NOTICE message from a user with this tag, they can display that message in the buffer specified in the tag, as if it was a channel message.
+
+To prevent abuse, client implementations might allow users to hide these messages when the sender does not belong to the specified channel.
+
+## Examples
+
+In this example, user `me` requests documentation from bots in channel `#chan`, then gets the response in private, but in the context of that channel, using `channel-context`.
+
+    C: PRIVMSG #chan :!help
+    S: @+draft/channel-context=#chan :bot!bot@bot NOTICE me :I'm helping.