Historical Rules · 11 November 2016
Rule 701.3b
Official source text from the 11 November 2016 Rules release
If an effect tries to attach an Aura, Equipment, or Fortification to an object it can’t be attached to, the Aura, Equipment, or Fortification doesn’t move. If an effect tries to attach an Aura, Equipment, or Fortification to the object it’s already attached to, the effect does nothing. If an effect tries to attach an object that isn’t an Aura, Equipment, or Fortification to another object or player, the effect does nothing and the first object doesn’t move.