Difference in allowed accelerator keys between Qt and Wx

There are a number of accelerator keys that the Wx backend allows that the Qt backend does not, for example symbols such as "-" and "=". Under Qt `key_event_to_name` maps them to 'Unknown-Key' because they are not explicitly listed in `key_map`, but under Wx there is a fall-back condition that passes through any key code accepted by `chr`.

Is this intended behaviour, perhaps enforcing a style guide, or an accident of history? :smile:

This was spotted under traitsui v6.0.0, but it looks like the issue affects all versions since (and I haven't checked earlier).