docs: def decode(self, encoding=None):
          ''' Returns a copy with all keys and values de- or recoded to match
              :attr:`input_encoding`. Some libraries (e.g. WTForms) want a
              unicode dictionary. '''
          copy = FormsDict()
          enc = copy.input_encoding = encoding or self.input_encoding
          copy.recode_unicode = False
          for key, value in self.allitems():
              copy.append(self._fix(key, enc), self._fix(value, enc))
          return copy