backend.filter.extendScopesBefore

Provides an opportunity to interact with the Filter widget before defining the filter scopes

Example usage:

Event::listen('backend.filter.extendScopesBefore', function ((\Backend\Widgets\Filter) $filterWidget) {
    // Just in case you really had to do something before scopes are defined
});

Or

$listWidget->bindEvent('filter.extendScopesBefore', function () use ((\Backend\Widgets\Filter) $filterWidget) {
    // Just in case you really had to do something before scopes are defined
});