anchor.diff:  }
   ----
   
  -In this example, we see that we billed for two units `cell-phone-minutes` and `Mbytes`: For the `cell-phone-minutes`, the quantity
  -recorded for the period was such, that we reached the maxium for tier 1 and started to bill some units for tier 2; for `Mbytes`, we billed 
  -everything in the tier 1. The amount reported is the sum of the amount : 40 + 2000 + 100 = 2140.
  +In this example, we see that we billed for two units `cell-phone-minutes` and `Mbytes`: For the `cell-phone-minutes`, the quantity recorded for the period was such, that we reached the maxium for tier 1 and started to bill some units for tier 2; for the `Mbytes` units, we billed  everything in the tier 1. The amount reported is the sum of the amount : 40 + 2000 + 100 = 2140.
   
   ==== Detail Mode
   
  
positive.code: }
  ----
  
  In this example we see that we were invoiced for 2 different units, provide details for each unit, and the amount that will be charged.
  Note that because unit `members` reached tier 3, the amount will be based on the pricing for that tier.
  
  ==== Consumable In Arrear Mode
  
  In this mode, we are going through tier level to compute the price based on the tier price and quantity.
  We can configure the invoicing system to output one item per tier, or one aggregate item for all tiers.
  
  ==== Agrregate Mode
  
  In the aggregate mode, we will see some json in the field `itemDetails`, to summarize the usage on a per tier basis and per unit basis:
  
  [source,bash]
  ----
  
negative.code: invoice item -- and the aggregate amount is computed by summing the sum amount. In order to activate this mode, one needs to set
  the system property `org.killbill.invoice.item.result.behavior.mode` to `DETAIL`.
  
  Each of the `USAGE` item will contain the following fields:
  
  * `quantity`: Quantity consumed for the unit (type) and on the given tier
  * `rate`: We reused the `rate` field normally reserved for `RECURING` type to output the price of the tier
  
  Also, the `itemDetails` json field will provide some additional details:
  
  [source,bash]
  ----
  