code: def add_header_check(self,
                           code=HEADER_CHECK_FAILED,
                           message=MESSAGES[HEADER_CHECK_FAILED]):
          
  
          t = code, message
          self._header_checks.append(t)
docs: Add a header check, i.e., check whether the header record is consistent
          with the expected field names.
  
          Arguments
          ---------
  
          `code` - problem code to report if the header record is not valid,
          defaults to `HEADER_CHECK_FAILED`
  
          `message` - problem message to report if a value is not valid