InsurancePlans that one subscribes to may include multiple "sub plans". One example is a medical plan that includes a drug plan (often provided by another payer through the payer that is being subscribed to). These memberPlan(s) need to be able to be referred to from InsurancePlan. These plans may be specific to a type of coverage (such as a dug plan), but may also include multi-type coverage. This should be considered when deciding where to place the element (at the root or under coverage).