The AJAX frontend appears to generate URLs like

https://server.local/registry-pe/api/v2/identifiers?person_id=3349&extended

where extended appears to update the query by adding the parent object to the contains. While not specifically prohibited by the RFC, a query string consisting of a label without a value isn't really a best practice, and it's also not completely clear what extended is supposed to do.

Minimally, this flag should become something like returnparent=true or related=parent. We should also discuss if this should be restricted to the AJAX API or if it should be part of the publicly documented REST API v2.