[New in this version]

The event ID is the reference hash of the event encoded using a variation of Unpadded Base64 which replaces the 62nd and 63rd characters with - and _ instead of using + and /. This matches RFC4648’s definition of URL-safe base64.

Event IDs are still prefixed with $ and might result in looking like $Rqnc-F-dvnEYJTyHq_iKxU2bZ1CI92-kuZq3a5lr5Zg.