Modifier keys ISO_Level3_Shift and ISO_Level5_Shift etc. insufficiently handled

Hi,

I know, I have already reported this bug
https://bugreports.qt.io/browse/QTBUG-18388
regarding ISO_Level5_Shift, but I think there is a more general issue that modifiers other than those listed in the KeyboardModifier enum
http://doc.qt.io/qt-5/qt.html#KeyboardModifier-enum
do not get handled properly (notably ISO_Level3_Shift (AltGr) and ISO_Level5_Shift, but maybe more). While ISO_Level3_Shift can be handled via
http://doc.qt.io/qt-5/qkeyevent.html#key
ISO_Level5_Shift can only be handled using
http://doc.qt.io/qt-5/qkeyevent.html#nativeModifiers

However, both do not make the situation bearable since this data is not used by the Qt shortcut system.

Is there any reason why these shifts are not included in the KeyboardModifier enum?

In Gtk it has never been a problem since …
https://developer.gnome.org/gtkmm/stable/group__gdkmmEnums.html#ga734c2979005c87dbe51223a0128cdd97
I am not sure if there is any difficulty in checking correctly which bits in the native modifiers correspond to ISO_Level3_Shift and ISO_Level5_Shift.

Illustration: As a consequence the text editor Kate is unusable for me, since it relies on the Qt shortcut system to handle navigation (before it used KF5/Qt5 it was a smaller problem, because the libkdeui shortcut system could handle ISO_Level3_Shift). Since I use ISO_Level3_Shift to access the arrow keys, pgup, pgdwn etc. with my keyboard layout, I cannot navigate in the usual way.

Regards