Allow multi-select in custom person/org field

Damon

Right now, you can add a customer field that allows you to reference a person or an org. But it is only single select. There are many scenarios where we'd like to multi-select one of these. For instance, we could have more than one Competitor (a list of which we maintain as Orgs) for a given customer. You can do a multi-select, but it's on a list of strings. I'd like to multi-select an entity like an org or person.