original_docstring: Validate the field's value of the header.
  
          Warnings and errors are then exposed through the
          ``validation_warnings`` and ``validation_errors`` properties.
          The ``has_warnings`` and ``has_errors`` properties should
          be used to test for the presence of warnings or errors.
          
docstring: Validate the field's value of the header.
docstring_tokens: Validate the field ' s value of the header .
code: def validate(self) -> None:
          """Validate the field's value of the header.
  
          Warnings and errors are then exposed through the
          ``validation_warnings`` and ``validation_errors`` properties.
          The ``has_warnings`` and ``has_errors`` properties should
          be used to test for the presence of warnings or errors.
          """
          now = datetime.now()
          earliest_valid_creation_date = now - timedelta(days=90)
          latest_valid_creation_date = now + timedelta(days=90)
          try:
              creation_date = datetime.strptime(self.creation_date, Date.DATE_FORMAT)
          except ValueError:
              self.add_error('creation_date', "INVALID: must contain a valid date.")
          else:
              if not earliest_valid_creation_date < creation_date < latest_valid_creation_date:
                  self.add_error('creation_date', "INVALID: creation date may not differ by +/- 90 calendar days"
                                                  " from the date when read in.")
  
          # XXX Properly validate bank clearing no. of the client can only be done with a reliable and up to date
          # database of bank clearing numbers, which is difficult to obtain.
code_tokens: def validate ( self ) -> None : now = datetime . now ( ) earliest_valid_creation_date = now - timedelta ( days = 90 ) latest_valid_creation_date = now + timedelta ( days = 90 ) try : creation_date = datetime . strptime ( self . creation_date , Date . DATE_FORMAT ) except ValueError : self . add_error ( 'creation_date' , "INVALID: must contain a valid date." ) else : if not earliest_valid_creation_date < creation_date < latest_valid_creation_date : self . add_error ( 'creation_date' , "INVALID: creation date may not differ by +/- 90 calendar days" " from the date when read in." )
short_docstring: Validate the field's value of the header.
short_docstring_tokens: Validate the field ' s value of the header .
comment: """Validate the field's value of the header.
  
          Warnings and errors are then exposed through the
          ``validation_warnings`` and ``validation_errors`` properties.
          The ``has_warnings`` and ``has_errors`` properties should
          be used to test for the presence of warnings or errors.
          """$SEP$# XXX Properly validate bank clearing no. of the client can only be done with a reliable and up to date$SEP$# database of bank clearing numbers, which is difficult to obtain.