doc(sdk): Document what happens when timeline event sending fails
@@ -351,6 +351,9 @@ impl Timeline {
/// If the encryption feature is enabled, this method will transparently
/// encrypt the room message if the room is encrypted.
///
+ /// If sending the message fails, the local echo item will change its
+ /// `send_state` to [`EventSendState::SendingFailed`].
+ ///
/// # Arguments
///
/// * `content` - The content of the message event.
