[bbanyc]

Yeah I remember as a kid saving a file with Word 97, then opening it on a different computer with Word 95, and there was a box between every pair of characters. Looking back, it's clear that the internal representation had changed from an 8-bit encoding to UTF-16 but I learned to be careful to "save as Word 95" every time from then on.

[blackoil]

That is forward compatibility and is much more difficult to maintain.