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

1  –  Syntax

  With an Attached handler:

      WHEN ERROR IN
          protected-statement
          [protected-statement,...]
         .
         .
         .
      USE
          handler-statement
          [handler-statement,...]
         .
         .
         .
      END WHEN

  With a Detached Handler:

      WHEN ERROR USE handler-name
           protected-statement
           [protected-statement,...]
          .
          .
          .
      END WHEN
      HANDLER handler-name
           handler-statement
           [handler-statement,...]
          .
          .
           .
      END HANDLER