def string_length_fraction(str_list_1, str_list_2):
    """
    Calculate the percentage difference in length between two strings, such that s1 / (s1 + s2)
    :param str_list_1: List of strings.
    :param str_list_2: List of strings.
    :return: Float (0 to 1).
    """
    str1_size = sum(sum(len(j.strip()) for j in i) for i in str_list_1)
    str2_size = sum(sum(len(j.strip()) for j in i) for i in str_list_2)

    return str1_size/(str1_size + str2_size)