Relation p3p#purpose (Statement,PurposeClass)  Defines the purpose for which the data practise is employed
  supertype:  P3P_relation (pm)
  subtype:  purposeAlways__purposealway (Statement,PurposeClass)  The purpose is always required; users cannot opt-in or opt-out of this use of their data.
  subtype:  purposeOptIn (Statement,PurposeClass)  Data may be used for this purpose only when the user affirmatively requests this use.
  subtype:  purposeOptOut (Statement,PurposeClass)  Data may be used for this purpose unless the user requests that it not be used in this way.