anchor.diff:  </tiers>
   ----
   
  -In the `CONSUMABLE` mode, when defining usage section with multiple unit (types), it is important to realize that the consumer *is charged independently
  -for each unit*, so for example, with the definition provided above:
  -
  -Given the following usage data for the period:
  +In the `CONSUMABLE` mode, when defining a usage section with multiple unit (types), it is important to realize that the consumer *is charged independently
  +for each unit*. For example, with the definition provided above, and given the following usage data for the period:
   
   * 1500 cell-phone-minutes
   * 2048 Mbytes
   
  -The total amount would be 739.4 and is calculated as follows;
  -
  -Each unit is billed separately as;
  +The total amount would be 739.4. This is calculated as follows:
   
   cell-phone-minutes:
   
  
positive.code: * The first `100` blocks of this size will be priced at 1.00 EUR
  * If a consumer uses more than `100` blocks of this size, he will be charged at the price of the next tier.
  
  As mentionned previously, such usage section can contain multiple tiers and also charge for multiple unit types.
  The following section shows the defintion for 2 units, *cell-phone-minutes* and *Mbytes*, and define two tiers.
  The `max` value for the last tier is defined with *-1* to allow for unbounded value:
  
  [source,bash]
  ----
  
negative.code: 
  ===== Consumable In Arrear Mode: `TOP_TIER`
  
  Using the same example from the previous section with the `TOP_TIER` policy would lead to a different result, since all charges would be calculated at the higher tier:
  
  * cell-phone-minutes: 150 blocks of size 10 at 0.50 EUR = 150 * 0.5 = 75
  * Mbytes: 2048 blocks of size 1 at 0.10 EUR = 2048 * 0.1 = 204.8
  
  So the total amount would be 279.8.
  
  ===== Capacity In Arrear Mode
  
  In the `CAPACITY` mode, each `tier` definition contains a list of `limit`, specifying the maximum value for this tier for each `unit` (type). *In contrast to the `CONSUMABLE` mode, the billing happens across the units*. Let's assume the following definition for one tier, with 2 different types of units, `bandwith-meg-sec` and `members`:
  
  [source,bash]
  ----
  