MSC3964: Notifications for room tags

proposals/3964-notifications-for-room-tags.md

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+# MSC3964: Notifications for room tags
+
+Users expect that a [room's tag](https://spec.matrix.org/v1.5/client-server-api/#room-tagging)
+has an impact on its notification settings. [^1]
+
+The "low priority" setting for rooms is often used in cases where a user
+doesn't want to leave a room, but also doesn't care about the room. Similarly,
+the "favorites" tag is used to mark rooms which a user *really* cares about.
+
+It is a source of confusion that users continue receiving notifications of all
+messages in rooms which are set to "low priority". And it is desirable to control
+the notification configuration for all rooms of the same tag at once. This would
+enable the following features:
+
+* Mark all low-priority rooms as mentions & keywords. [^2]
+* Set all favorites to notify for all message.
+* Set all "work" rooms as "mute" (assuming the user has a custom "work" tag).
+
+An additional benefit of being able to control notifications per room tag is that
+the total number of push rules per user can be reduced. Instead of having a push
+rule per low-priority room, a single rule would suffice. This is useful to limit
+the processing effort of push rules as well as reducing the overall size of
+`/sync` responses.
+
+## Proposal
+
+### A new push rule condition for room tags
+
+A new [push rule condition](https://spec.matrix.org/v1.5/client-server-api/#conditions-1)
+is proposed. The `room_tag` push condition has a single parameter: `pattern`
+which is a glob-style pattern to match against the room tags of the room. If any
+single room tag matches the pattern then the room condition matches. (Globbing is
+performed in the same way as the `event_match` condition.)
+
+If the `pattern` property is not provided then the condition matches against
+untagged rooms.
+
+For example, given a room with tags:
+
+```json
+{
+  "content": {
+    "tags": {
+      "m.favourite": {
+        "order": 0.1
+      },
+      "u.work": {
+        "order": 0.9
+      }
+    }
+  },
+  "type": "m.tag"
+}
+```
+
+This would match a push rule like:
+
+```json
+{
+  "actions": [
+    "notify",
+    {
+      "set_tweak": "sound",
+      "value": "default"
+    },
+    {
+      "set_tweak": "highlight"
+    }
+  ],
+  "conditions": [
+    {
+      "kind": "room_tag",
+      "pattern": "m.favourite"
+    }
+  ],
+  "rule_id": "favourites",
+  "enabled": true
+}
+```
+
+### A new default push rule for low-priority rooms
+
+By default, low-priority rooms would be set "Mentions & Keywords" by default;
+this would be done by adding a new `underride` rule:
+
+```json
+{
+  "rule_id": ".m.rule.suppress_lowpriority",
+  "default": true,
+  "enabled": true,
+  "conditions": [
+    {
+      "kind": "room_tag",
+      "pattern": "m.lowpriority"
+    }
+  ],
+  "actions": []
+}
+```
+
+## Potential issues
+
+None foreseen.
+
+## Alternatives
+
+### Per-space notifications
+
+Per-space notification configuration has been touted as an alternative. The author
+sees these are complementary features.
+
+### Tag matching
+
+The `room_tag` condition only has to match a single tag in order to match, it
+might make sense to consider the tag ordering, but it is not clear what impact
+that would have on the proposal (since push rules are already ordered).
+
+## Security considerations
+
+N/A
+
+## Unstable prefix
+
+`org.matrix.msc3964.room_tag` should be used instead of `room_tag` for the push
+rule condition.
+
+`.org.matrix.msc3964.suppress_lowpriority` push rule ID should replace the new
+`.m.rule.suppress_lowpriority` default push rule.
+
+## Dependencies
+
+None.
+
+[^1]: https://github.com/vector-im/element-web/issues/16836
+[^2]: https://github.com/vector-im/element-web/issues/915, https://github.com/vector-im/element-meta/discussions/873