Support multiple default values in case of relationships or repeatables

[JoryHogeveen]

Problem to Solve

https://wordpress.org/support/topic/how-to-populate-a-relationship-field-as-a-list-with-more-than-one-avlue/

We currently only allow a single default value.

Proposed Solution

1. Maybe we could make the default value a repeatable field?
2. Another option is to explode the default value by predefined separator in case it's a multi-value field
3. Or we could allow JSON input?

Possible Workaround

Currently you can only use PHP filters I suppose.