As I am finishing putting property look-up together for the Unicode library GSoC, I am wondering what kind of binary compatibility it should aim for. The work from Graham Barnett back in 2005 defined an abstract base class with virtual functions for every unicode-related feature but I believe that's overkill. Basically, the current property design I have is like this struct some_property { enum type { some_default, some_value1, some_value2, ... _count; } }; some_property::type get_some_property(char32 ch); With get_some_property a simple look-up in the table, but the table layout being version dependent it would need to be in the library TUs. However, a new version of the library may return a value that is not within the enum. Should it then work like this? some_property::type get_some_property(char32 ch) { some_property::type p = get_some_property_impl(ch); if(p >= some_property::_count) return some_property::some_default; return p; } some_property::type get_some_property_impl(char32 ch); Is that suitable? Or do we want more/less flexibility? Apart from that, expect a documentation update by the end of the week.