[my]power / [my]rawpower
Checks whether or not you (mypower) or the specified target (power) has the given amount of its power type.
Parameters
A less than <
or greater than >
sign followed by the amount of actual power
([my]rawpower) or the percentage ([my]power) that is required.
Examples
/cast [mypower>60] Heroic Strike
Will cast Heroic Strike when you have more than 60% rage.
/cast [harm @target power>10] Mana Burn
Will cast Mana Burn as long as your current target has more than 10% power.
/cast [myrawpower<390] Arcane Explosion(Rank 1); Arcane Explosion
Will cast max rank Arcane Explosion as long as you have the mana to do so and will cast Arcane Explosion Rank 1 when you don't.