Progress: Continue work on the write functions.

Progress: Continue work on the write functions.

This is in the middle of changing the logic in `private_fl_fss_basic_write()`.

I noticed that I was forgetting to handle the `F_bound` case for a joiner where the character to the right no longer can be processed.
I need to verify that I did this for the read functions.
I need to add unit tests for catching these cases as well, if I have not done so already.