code: public Matrix4f set3x3(Matrix3fc mat) {
          if (mat instanceof Matrix3f) {
              MemUtil.INSTANCE.copy3x3((Matrix3f) mat, this);
          } else {
              set3x3Matrix3fc(mat);
          }
          properties &= ~(PROPERTY_PERSPECTIVE | PROPERTY_IDENTITY | PROPERTY_TRANSLATION | PROPERTY_ORTHONORMAL);
          return this;
      }
docs: Set the upper left 3x3 submatrix of this {@link Matrix4f} to the given {@link Matrix3fc} and don't change the other elements.
  
  @param mat
  the 3x3 matrix
  @return this