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=====Subjects, Effects, and Areas=====

If the spell affects creatures directly the result travels with the subjects for the spell’s duration. If the spell creates an effect, the effect lasts for the duration. The effect might move or remain still. Such an effect can be destroyed prior to when its duration ends. If the spell affects an area then the spell stays with that area for its duration. 

Creatures become subject to the spell when they enter the area and are no longer subject to it when they leave.