This class represents an invoice or bill for a Billable Service. A single Billable Service may have multiple Billing Events due to the coordination of multiple payers (e.g.,, Health Plan A is billed for 70%, Health Plan B is billed for 20%, and the Patient is billed for the remaining 10%), and a single Payer may be billed multiple times as payment is negotiated electronically (e.g., the Payer might initially reject a bill, and may accept it upon submission of a second bill containing more information).