Just a feedback to the non-prefixed ones: -----Ursprüngliche Nachricht----- Von:David Brown via Std-Proposals <std-proposals_at_[hidden]> So for non-prefixed attributes, I don't see a situation where ignorable attributes are ever appropriate - though some can have implementation-defined behaviour which is "do nothing". If currently attributes are ignorable, especially non-prefixed ones (i.e. with valid syntax today), they should not suddenly start to be hard errors. Otherwise programs need #if conditionals for each use of an attribute to test for the C++ standard.