Looking at the Nuklear example code again it turns out that I was remembering wrong. I seemed to remember that Nuklear requires to store persistent state on the API user side and pass that into the Nuklear functions, but this was actually microui 1.x (which also has been fixed in the meantime in microui 2.x).

Sorry about the confusion.

E.g. in microui 1.x defining a window worked like this:

    static mu_Container window;
    if (mu_begin_window(ctx, &window, "Style Editor")) { ... }

...in microui 2.x it's no longer necessary to store the window state on the user side:

    if (mu_begin_window(ctx, "Style Editor", mu_rect(350, 250, 300, 240))) { ... }