docs: def clean_value(self, value):
          '''
          Additional clean action to preprocess value before :meth:`to_python`
          method.
  
          Subclasses may define own clean_value method to allow additional clean
          actions like html cleanup, etc.
          '''
          # We have to clean before checking min/max length. It's done in
          # separate method to allow additional clean action in subclasses.
          if self.nontext_replacement is not None:
              value = replace_nontext(value, self.nontext_replacement)
          if self.strip:
              value = value.strip()
          return value