def split_all(s, chars):
    """Split on multiple character values.

    >>> split_all('a_b_c_d', '_. ')
    ['a', 'b', 'c', 'd']
    >>> split_all('a b c d', '_. ')
    ['a', 'b', 'c', 'd']
    >>> split_all('a.b.c.d', '_. ')
    ['a', 'b', 'c', 'd']
    >>> split_all('a_b.c d', '_. ')
    ['a', 'b', 'c', 'd']
    >>> split_all('a b_c.d', '_. ')
    ['a', 'b', 'c', 'd']
    """
    chars = list(chars)

    o = [s]
    while len(chars) > 0:
        c = chars.pop(0)

        n = []
        for i in o:
            n += i.split(c)

        o = n
    return o