code: public Matrix3f set(Matrix4fc mat) {
          if (mat instanceof Matrix4f) {
              MemUtil.INSTANCE.copy((Matrix4f) mat, this);
          } else {
              setMatrix4fc(mat);
          }
          return this;
      }
docs: Set the elements of this matrix to the upper left 3x3 of the given {@link Matrix4fc}.
  
  @param mat
  the {@link Matrix4fc} to copy the values from
  @return this