If you want to execute the four components a, b, c, and d in sequence, you can use the THEN keyword. It should be noted that THEN must be capitalized.

<chain name="chain1">
    THEN(a, b, c, d);
</chain>

Of course, if you write it nested, it is equivalent to the above

<chain name="chain1">
    THEN(a, b, THEN(c, d));
</chain>

Flow chart