In Kibana, dashboards can be built with visualisations inside stored by value or by reference. Historically only by reference was supported so most of our dashboards still use by reference. The goal is to move to by value to have dashboards and visualisations directly bundled together as a unit which speeds up the installation of it in Fleet and also makes sure the visualisations do not all show up in the search, only the dashboard.

To help with this effort and notify engineers about usage of by reference, it would be nice if during building a package, package-spec or the build process would show a warning if a visualisation in a dashboard is added by reference instead of by value. Changes should not be blocked on this but engineers notified about it.

This is related to elastic/kibana#129303 which should help engineers with an easy migration to by value.