Periodicity is a key component to working with plans and powers the billing relationship.

Periodicity is comprised of three attributes: type, duration, and cents. A periodicity's type must be one of: day, week, month, or year. The periodicity's duration multiplied by its type determines its total length.

To charge someone $14.99 every month, you would create a plan with a periodicity where: type=month, duration=1, and cents=1499.
To charge someone $24.99 every quarter, you would create a plan with a periodicity where: type=month, duration=3, and cents=2499.

Frequently you will want to provide some sort of introductory pricing (whether a free trial period or a discounted initial period). This will be outlined in discounts and offers. But the plan is defined based on the recurring charge, without consideration of any promotional period.

This will allow you to create (and test) many different types of offers to see what resonates. All without having to duplicate plans or plan groups.

Attributes:

Name	Type	Description
type	string	One of: `day`, `week`, `month`, or `year`.
duration	integer	The multiple against `type` that defines the total period length.
cents	integer	How much to charge for the period duration.