Yeah, I could see that would be the case that would likely break if it's violated. Making anything better opt-in sounds all great and well till we end up in th

Yeah, I could see that would be the case that would likely break if it's violated. Making anything better opt-in sounds all great and well till we end up in this position again whereby we rely on one (or more) browser's unspecified line-breaking algorithm for the "better line-breaking" option. If we specify anything, we probably actually need to specify the algorithm (and given AFAIK there hasn't been notable improvements in decades, that probably isn't the end of the world).