Sure, I'll give the particular example of bash compared to sh is probably a poor example to put focus on in that it's one that doesn't demonstrate every point j

Sure, I'll give the particular example of bash compared to sh is probably a poor example to put focus on in that it's one that doesn't demonstrate every point just like SDL 1.2 to 2.0 wouldn't due to SDL_Compat (leaving some room for interpreted vs compiled differences to not count otherwise we'd have to restrict conversation to scripted GUIs instead of QT or compiled shell commands instead of scripts). The other example of ncurses 6 vs 5 is better as it's a compiled interface where the ABI broke but that was already in the comment. Or take the other example zsh vs bash on how there are often changes that take some porting work but not much. More than each of the specific examples, the main point was meant to be more around things like stdout being comparable to display server protocols which do behave about the same in compatibility. Specific apps end up doing their own thing with compatibility regardless which interface they output on. One of the examples I chose was a poor example for that and seems to have distracted from that point, mea culpa. Another commenter noted Python might have been a better example of scripting compatibility over time.