Invincible PVE Group (A New Twist on a Classic)

[valle2000]

#show earth shield
/target Tank
/castsequence [@targettarget, exists] flame shock, lightning bolt, lightning bolt
/castsequence [@Tank] reset=combat earth shield, null
/cast [@Tank] riptide

This macro looks interesting.
However I'm no expert so I'm wondering can the same be used with a priest to assist with holy fire,smite and at the same time making sure tank is shielded and renewed?

But what happens exactly when the macro is activated? If tank has a target, won't the result be only the dps-spell is cast and the others lines will be rejected due to "can't do that yet"?