def string_in_list(_string, _list):
    """Case insensitive search for string in list
    returns the matching list value
    >>> string_in_list("Brack",["bar", "bracK", "foo"])
    'bracK'
    >>> string_in_list("foo", ["FFO", "FOO", "foo2", "foo3"])
    'FOO'
    >>> string_in_list("foo", ["FFO", "foo2", "foo3"])
    """
    for x in _list:
        if _string.lower() == x.lower():
            return x
    return None