code: def unquote_string(self, string):
          
          value = string[1:-1]
  
          forbidden_sequences = {ESCAPE_SUBS[STRING_QUOTES[string[0]]]}
          valid_sequences = set(ESCAPE_SEQUENCES) - forbidden_sequences
  
          for seq in ESCAPE_REGEX.findall(value):
              if seq not in valid_sequences:
                  raise self.error(f'Invalid escape sequence "{seq}"')
  
          for seq, sub in ESCAPE_SEQUENCES.items():
              value = value.replace(seq, sub)
  
          return value
docs: Return the unquoted value of a quoted string.