code: function fromMat4(out, a) {
    out[0] = a[0]
    out[1] = a[1]
    out[2] = a[2]
    out[3] = a[4]
    out[4] = a[5]
    out[5] = a[6]
    out[6] = a[8]
    out[7] = a[9]
    out[8] = a[10]
    return out
  }
docs: Copies the upper-left 3x3 values into the given mat3.
  
  @alias mat3.fromMat4
  @param {mat3} out the receiving 3x3 matrix
  @param {mat4} a   the source 4x4 matrix
  @returns {mat3} out