A flag to set to indicate the preferred telephone number for the person or organisation from whom the specimen was acquired.
The telephone number marked as preferred by means of this attribute should be the first approached. The other telephone numbers should be regarded as alternative numbers.
Recommended or Prescribed Values
true, false, or empty. For a single unbounded element there should only be one with the @preferred attribute set to true.
The element with its attribute set to true is the preferred telephone number.