docs: function scaleAndAddRow (m, srcRow, destRow, scale) {
    const me = m.elements;
    let i = destRow;
    let j = srcRow;
    let alpha = (scale === undefined ? 1.0 : scale);
    me[i] += me[j] * alpha;
    me[i + 3] += me[j + 3] * alpha;
    me[i + 6] += me[j + 6] * alpha;
  }