The meta object contains meta-information describing the event: when it was created, where it came from, its type et cetera. The meta object contains the same members regardless of meta.type1, with the caveat that certain members are optional and the tendency to use them may vary with event type.
Even though the meta object is kept universal for all event types, it may change over time as the Eiffel protocol evolves. Due to the per-event versioning of the protocol, this means that different unique combinations of event type and version may feature different meta object syntax. Consequently, the syntax is described in the documentation of each respective event type.
1: Event types are versioned independently from one another. There are three important consequences of this. First, any change to meta requires all events to be updated. Second, any schema of a specific version of an event must also include the meta object – specifically as it is defined for that version of the event. Third, consumers should be prepared to receive events of varying meta contents. The exception to this are the meta.type and meta.version fields, which are always assumed to be present change.