Thanks @woky for telling us about this. Currently I work on refactoring all the windowing code, so consider this on my todo list when I continue the work on the qt backend.

In your opinion, should all matplotlib windows have the same class, or should we differentiate between plot windows and other windows such as the subplot config window?

@OceanWolf Thank you for your efforts.

All programs I've checked so far use one only single class name (well, two, but both same). For instance all Octave figures have

WM_CLASS(STRING) = "Octave", "Octave"

which is fine because Octave GUI elements I use are only figures which I want floating most of time. However, in some programs I wish for different types of windows to have different classes (for instance to make diff window floating in Intellij IDEA). As far as I know all sane tiling WMs can match class by wildcard or regex so if all classes started with matplotlib_ it'd still be easy to match all matplotlib windows (or perhaps more classes could be used). But for me, there'd not be much use for it here as I want all figure related windows floating. So I think it should be what you find most simple and elegant =).

I looked into doing something about this awhile ago and got lost in the details of where you set this in pyqt.

I don't know if any of the other backends do this either.

some backends do set something, others do not (notably the qt4agg backend doesn't set anything)

This is also valid for the Qt5Agg in recent matplotlib versions.

Should be closed by #8394 (except for WX which doesn't expose such an API at all, and for macos where it isn't even clear that WM_CLASS exists at all). Feel free to reopen if a solution appears for WX or if this is actually useful on OSX as well.