ReadonlysidSession ID (or actor ID, site ID, process ID, etc.), a random identifier randomly assigned to each editing session.
Length of the logical time interval.
Logical time (or sequence number, tick, etc.), a monotonically increasing integer, starting from 0. It does not produce gaps on local machine, but it can produce gaps when merged with other clocks.
Needs to be mutable in vector clock. Other than that, it should be treated as immutable.
Similar to ITimestamp, but represents a logical time interval, instead of just a single time point.