docs: def unquote_header_value(value, is_filename=False):
      r"""Unquotes a header value.  (Reversal of :func:`quote_header_value`).
      This does not use the real unquoting but what browsers are actually
      using for quoting.
  
      .. versionadded:: 0.5
  
      :param value: the header value to unquote.
      """
      if value and value[0] == value[-1] == '"':
          # this is not the real unquoting, but fixing this so that the
          # RFC is met will result in bugs with internet explorer and
          # probably some other browsers as well.  IE for example is
          # uploading files with "C:\foo\bar.txt" as filename
          value = value[1:-1]
  
          # if this is a filename and the starting characters look like
          # a UNC path, then just return the value without quotes.  Using the
          # replace sequence below on a UNC path has the effect of turning
          # the leading double slash into a single slash and then
          # _fix_ie_filename() doesn't work correctly.  See #458.
          if not is_filename or value[:2] != "\\\\":
              return value.replace("\\\\", "\\").replace('\\"', '"')
      return value