The WHEN ERROR statement marks the beginning of a WHEN ERROR  construct.
  The  WHEN ERROR construct contains a protected region and can include an
  attached or detached handler.

  Examples

  WHEN ERROR IN
      INPUT "Enter your hourly rate";hourly_rate%
           .
           .
           .
  USE
      SELECT ERR
           .
           .
           .
      END SELECT
  END WHEN

  WHEN ERROR USE error_trapper
       INPUT "Enter your hourly rate";hourly_rate%
           .
           .
           .
  END WHEN
  HANDLER error_trapper
           .
           .
           .
  END HANDLER