code: def add_validator(self, name, validator, *args, **kwargs):
          
          if name in self._dyn_fields:
              if 'validators' in self._dyn_fields[name]:
                  self._dyn_fields[name]['validators'].append(validator)
                  self._dyn_fields[name][validator.__name__] = {}
                  if args:
                      self._dyn_fields[name][validator.__name__]['args'] = args
                  if kwargs:
                      self._dyn_fields[name][validator.__name__]['kwargs'] = kwargs
              else:
                  self._dyn_fields[name]['validators'] = []
                  self.add_validator(name, validator, *args, **kwargs)
          else:
              raise AttributeError('Field "{0}" does not exist. '
                                   'Did you forget to add it?'.format(name))
docs: Add the validator to the internal configuration dictionary.
  
          :param name:
              The field machine name to apply the validator on
          :param validator:
              The WTForms validator object
          The rest are optional arguments and keyword arguments that
          belong to the validator. We let them simply pass through
          to be checked and bound later.