That looks very inflexible for later edits, marking characters or words means a potentially cumbersome recounting if something is reworded or just if a typo is

That looks very inflexible for later edits, marking characters or words means a potentially cumbersome recounting if something is reworded or just if a typo is fixed. Also, I get the second and subsequent number issue are the three locations to highlight, but what instruction does the first, -6:-3, give to the formatter in your example?