Let's say that a person's eligibility for a product is based on whether that person is "low-waged".
Initially, legislation is enacted which lays down that a person is considered to be "low-waged" if that person's total pre-tax income is less than $20,000 per annum.
However, after some successful lobbying, the legislation is revisited and it is agreed that from 2001 onwards, a person will instead be deemed to be "low-waged" based on whether that person's post-tax income is less than $15,000 per annum.
After a change in administration, the legislation comes under scrutiny again, and from 2002 revised legislation takes effect which broadens the low-income net to cover persons with pre-tax income less than $22,000 per annum and/or post-tax income less than $16,000.
The initial eligibility calculation (for a person) is based directly off the pre-tax income (for that person). When the agency implements the changes in legislation, then a rule set designer changes the initial implementation to instead use the legislationChange expression to combine contributions from the different legislation "eras". (The implementation of the initial era is just that for the initial implementation; there are new implementations for the subsequent eras.)
John Smith makes a claim for benefit. John's income levels are as follows:
John's eligibility varies not only according to the variations in his income levels, but also according to the changes in legislation that are enacted: