Thank you very much for this wonderful module!
Currently it's focused on providing a Field Widget for Checkall, but the next and more general step would be to extend the Drupal Core Checkboxes Element with a '#checkall' => TRUE option.
That way it could also be used for custom developments and not only for field widgets.
Furthermore, the field widget could then simply use this new element.
The final goal should be to have this prepared to move into core! :)
Active
1.0
Code
@Maintainers: ✨ Add a '#selectall' option for checkboxes element Active is RTBC now, so it might be the right time to link the issue on the module page and eventually prepare an update path to the core solution?
The module might then become obsolete and could uninstall itself.