Says whether two complex subjects match (SSF 1.0 section 8.1.3.1): every member both define is identical, and at least one is defined by both.
Optional
the subject on the stream
the event's subject
true when they match
Says whether two complex subjects match (SSF 1.0 section 8.1.3.1): every member both define is identical, and at least one is defined by both.