This should probably be done at the source of this external file, but I couldn't find where that is. Perhaps it should be mentioned in the file header comment?
Rewrote main wrapping loop. Now uses iterators instead of indices and intermediate strings.
Differentiates between chars to wrap before, after or instead of.
Doesn’t preserve trailing newlines.
Wraps or more characters.
Dropped support for using tab character as an indent setting control char.
Hopefully avoids all the undefined behaviour and other bugs of the previous implementation.