cms.template.processSettingsBeforeSave

Fires before a CMS template (page|partial|layout|content|asset) is saved and provides an opportunity to interact with the settings data. $dataHolder = {settings: []}

Example usage:

Event::listen('cms.template.processSettingsBeforeSave', function ((\Cms\Controllers\Index) $controller, (object) $dataHolder) {
    // Make some modifications to the $dataHolder object
});

Or

$CmsIndexController->bindEvent('template.processSettingsBeforeSave', function ((object) $dataHolder) {
    // Make some modifications to the $dataHolder object
});