Custom data associated with this Billing Plan.
Custom Data is stored in CashBox as a pair of matched text strings, called name-value pairs. You can assign custom data to Billing Plans, Rate Plans, Products, Season Sets, Subscriptions and Accounts, each of which is associated with its own Custom Data list. For each of these Objects, CashBox stores a list of Names, which you associate with text string Values. You can use these name-value pairs to categorize and sort aspects of your system.