Is it Matrix4 or Quaternion that Three.js finally uses?

Re: Object3dD.applyMatrix4() or Object3dD.applyQuaternion().
I assume applying one will update the other.
So which does Three.js finally use at the low GL level?

My knowing this will not affect me in any way other than to make me feel good.

What effectively goes into the shader are matrices. The most common one is the so called “world matrix” which represents the position, rotation and scale of a 3D object in world space combined into a single 4x4 transformation matrix.

Thank you. I could joke about what took you so long to answer (3 min) but I won’t.