Dear Edward, throughout this thread you keep saying that you or the user will not understand what "dropping c++03 support" means and I have to say I find that very hard to believe, as the concept of "XXX is not supported" is ubiquitous throughout software development. There are of course differences in detail, but universally it always means something along the lines of "We don't promise that XXX works. When you try XXX you are on your own, we take no responsibility for what happens if you do and even if it works now, it might not work with the next product version (even if it is just a minor/path update)." Now, on top of that, "XXX is not supported" often means that "XXX really just doesn't work", but I can give you dozens (probably thousands) of examples where things that are not officially supported happen to work e.g.: - Forward declaring anything from namespace std or defining anything inside std is UB, yet many libraries (inside and outside of boost) do it anyway and "it works" - Microsoft's WSL currently doesn't support running graphical applications, however, users have been using it to successfully run various Linux DMs for quite some time now - Many libraries (inside and outside of boost) have a list of supported compilers. Does that mean they don't work with any compiler not mentioned on that list? Probably not (if I try a newer version of gcc or msvc, it most of the time still works) - they are just the compilers the author cares about and/or has tested so far. - Abseil.io has a very clear policy of what platforms and compilers are supported (https://abseil.io/docs/cpp/platforms/platforms) but again, there exist other platform/compiler combinations that will probably work just as well. - Intel's drivers for consumer lan chips don't support windows server, but if you manually circumvent the check, they work quite well. So really, the concept of it happens to work but isn't supported shouldn't be foreign to anyone active in software development or IT in general.