MSC3283: Expose capabilities for profile actions

proposals/3283-enable_set_displayname-capabilities.md

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+# MSC3283: Expose enable_set_displayname in capabilities response 
+
+
+Some home servers like synapse can be configured to enable_set_displayname: false. To enable clients to handle that gracefully in the UI this setting should be exposed.
+
+## Proposal
+
+The `/_matrix/client/r0/capabilities` endpoint could be decorated to provide more information on capabilities.
+```javascript
+{
+  "capabilities": {
+    "m.set_displayname": { "enabled": false },
+    "m.room_versions": {...},
+  }
+}
+```
+As part of this MSC, a capability will be added that exposes the server setting:
+`m.enable_set_displayname`
+
+## Client recommendations
+When presenting profile settings, clients should use capabilities in order to display the correct UI.
+If capability is not present the default is true.
+
+## Unstable prefix
+Implementations won't actually be able to use m.enable_set_displayname until the MSC has finished the Final Comment Period. While the MSC is in review, implementations can use an unstable prefix (im.vector.enable_set_displayname) instead.