FLTK should probably rename the key "Super" as well to be consistent. When it was made I expected X to call that key "Meta".
For some reason, the Weston documentation uses "Super" to name the default modifier key it uses,
e.g., man weston.ini contains :
sets the modifier key used for common bindings (string), such as
moving surfaces, resizing, rotating, switching, closing and set‐
ting the transparency for windows, controlling the backlight and
zooming the desktop. See weston-bindings(7). Possible values:
none, ctrl, alt, super (default)
That's also how W.B. called it in his message dated June 12th above, which has also been my first read
ever of such a key name.
Fortunately, that business is strictly private to the Weston compositor. FLTK doesn't have to process such a key stroke,
which is defined by Weston and can be changed via file $HOME/.config/weston.ini. The other Wayland compositor
I know, Mutter, doesn't use a key stroke to gain access to minimized windows.
In short, the Wayland FLTK platform doesn't use the key name "super" anywhere.