Publishes an event to one or more channels of a Realtime app. Listing several channels broadcasts the event to all of them in one call. Connected clients subscribed to those channels receive it in real time. The event name clients bind to. Application event names are free-form; the `bird:` and `bird_internal:` prefixes are reserved for the protocol and rejected. The channels to deliver the event to (up to 100 per call). Prefix with `private-` or `presence-` for authenticated channels. Arbitrary JSON payload delivered as the event data — an object, array, or scalar. Cap: 10 KB serialized. Exclude this connection from delivery, to avoid echoing a change back to the client that triggered it. The value is the client's connection id, assigned when its connection is established. Per-channel attributes to return alongside the publish, reflecting each channel's state at publish time (same semantics and validation errors as on the channel endpoints: `member_count` is presence-channels only, `connection_count` requires the app's connection-counting flag). Requesting attributes counts as one additional message toward usage. Per-channel attributes at publish time, present only when the request asked for them via `include`; one item per distinct target channel, sorted by name. Distinct members (presence channels only; requires include=member_count). Connections currently subscribed to this channel (requires include=connection_count and the app's connection-counting flag). Channel-scoped — distinct from the app-wide peak connections metric. A Realtime channel name. Only letters, digits, and _ - = @ , . ; Prefix with `private-` or `presence-` for authenticated channels.