### Rich replies

{{% changed-in v="1.3" %}}
{{% changed-in v="1.13" %}}

Rich replies are a
special kind of [relationship](#forming-relationships-between-events) which
effectively quotes the referenced event for the client to render/process how
it wishes. They are normally used with [`m.room.message`](#mroommessage) events.

{{% boxes/note %}}
Until v1.3 of the spec, rich replies were limited to `m.room.message` events
which could represent an HTML-formatted body. As of v1.3 this is now expanded
to *all* event types by dropping the requirement that an HTML-formatted body
be included.

Additionally, a rich reply can reference any other event type as of v1.3.
Previously, a rich reply could only reference another `m.room.message` event.
{{% /boxes/note %}}

{{% boxes/note %}}
{{% changed-in v="1.13" %}}
In previous versions of the specification, rich replies could include a fallback
format in the `body` and `formatted_body` for clients that do not support rich
replies, this is no longer the case. Clients might still want to remove this
fallback before rendering the event.

To strip the fallback on the `body`, the client should iterate over each
line of the string, removing any lines that start with the fallback
prefix ("> ", including the space, without quotes) and stopping when
a line is encountered without the prefix. This prefix is known as the
"fallback prefix sequence".

To strip the fallback on the `formatted_body`, the client should remove
the entirety of the `mx-reply` tag.
{{% /boxes/note %}}

Though rich replies form a relationship to another event, they do not
use `rel_type` to create this relationship. Instead, a subkey named `m.in_reply_to`
is used to describe the reply's relationship, leaving the other properties of
`m.relates_to` to describe the primary relationship of the event. This means
that if an event is simply in reply to another event, without further relationship,
the `rel_type` and `event_id` properties of `m.relates_to` become *optional*.

An example reply would be:

```json5
{
  "content": {
    "m.relates_to": {
      "m.in_reply_to": {
        "event_id": "$another_event"
      }
    },
    "body": "That sounds like a great idea!"
  },
  // other fields as required by events
}
```

Note that the `event_id` of the `m.in_reply_to` object has the same requirements
as if it were to be under `m.relates_to` directly instead.

#### Mentioning the replied to user

In order to notify users of the reply, it may be desirable to include the `sender`
of the replied to event and any users mentioned in that event. See
[user and room mentions](#user-and-room-mentions) for additional information.

An example including mentioning the original sender and other users:

```json5
{
  "content": {
    "m.relates_to": {
      "m.in_reply_to": {
        "event_id": "$another_event"
      }
    },
    "body": "That sounds like a great idea!",
    "m.mentions": {
      "user_ids": [
        // The sender of $another_event.
        "@alice:example.org",
        // Another Matrix ID copied from the m.mentions property of $another_event.
        "@bob:example.org"
      ]
    }
  },
  // other fields as required by events
}
```