I want to know if there is any way to show in a contact's card the groups where its email is added. I know that if I search for that email address in the results I will get the contact and the groups where that email is listed, but I have been requested for the other way.

Is there any documentation about adding new fields to the contacts??

Now another question. What would be the correct way to search for contacts "not added" to any group?? Is it possible using the search engine??