Detailed Behavior

Each instance of legislationChange must:

• specify the data type of the intervals in the timeline returned; and
• specify one or more eras of legislation, including an "initial" era (valid from the start of time, i.e. a null date). Each era must return a timeline of the same value type as that returned by the overall legislationChange expression

When an instance of legislationChange is evaluated, each era is evaluated and the resultant timelines are "spliced together" according to their era dates. An overall return timeline is assembled from these era-contributions, and this return timeline obeys the usual semantics of Timelines in general (in particular, identical contiguous values in the timeline will be amalgamated into a single value).

As such, if a particular change in legislation does not affect a calculation, then the resultant timeline will not change value on the legislation change date.