An added level of difficulty is understanding the order of the text in a broken TextSpanner in relation to the code.
Furthermore, a null value, or string with a space (" ") added to the 2nd text
right-broken.text
overwrites its default value right.text
. And this is especially more common and probable in scores with fewer systems per page, e.g. orchestral scores, music for band.
See Gould, Behind Bars: "Indicating continuing tempo change", page 185.