What does the 'Add' tag mean in Riftbound, specifically in the context of Kaisa's ability that adds universal power?

Ruling: The 'Add' tag means you're adding that resource to your temporary rune pool, which must be spent or it will go away at the end of the turn or at the draw phase. The universal power symbol means you can spend it on power costs of any domain (color), whereas power is normally generated by recycling a rune of the appropriate color.

Nuances:

• You can't respond to add abilities and they don't pass focus
• The resource is temporary and disappears if not used by end of turn or draw phase