The Big Picture of Rate Component Eligibility Rules
You can use eligibility rules to define the criteria when a rate component should be applied (or skipped). For example,
You may have a rate component that calculates an employee discount. This rate component may have eligibility criteria that require the person to have a given characteristic type and value (this assumes you use a person characteristic to identify employees) before the rate component is applied.
You may have a rate component that calculates a surcharge if the customer uses 25% more than they used in the same period in prior year.
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Note: 
Eligibility rules are optional. If you put eligibility rules on a rate component, the rate component will be skipped or applied as per the instructions in the rules. If you don't put eligibility rules on a rate component, the rate component will be executed (i.e., rate components are eligible by default).
The topics in this section describe eligibility rules.