Say you have a widget that has 3 commands: list, start and stop.
With one of those completion files widget stop <tab> will show you a tab-able list of widgets which are running.
So the source of the image can be decided on pull. Some more on this https://www.redhat.com/en/blog/manage-container-registries
It looks like it's ordered by priority.
unqualified-search-registries = ['registry.fedoraproject.org', 'registry.access.redhat.com', 'registry.centos.org', 'docker.io']