def unquote_header_value(value, is_filename=False):
    """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.

    :param value: the header value to unquote.
    :rtype: str
    """
    if value and value[0] == value[-1] == '"':
        value = value[1:-1]
        if not is_filename or value[:2] != '\\\\':
            return value.replace('\\\\', '\\').replace('\\"', '"')
    return value
