Hi! I looked at boost::system and some things are unclear to me: if error_code and error_condition are low level and abstract versions of the same category, then if error_condition::message simply returns |category().message( value() )| then how does category know that it's a condition value and not an error value? (error_code::message also returns| category().message( value() ))| currently error_condition appears quite useless to me since the values have to be the same as in error_code. by the way msdn tells us that error_code is for system errors and error_condition is for user-defined errors but this may be as true as unicode is equivalent to utf16 ;-) another problem I see in system_error::what(). i think it's common sense that what() should return - standarsized strings across platforms - english strings and is used only for lookup. but the current implementation returns the translated string of the underlying operating system. -Jochen