When a field is a RelationReference, ValueRelation and ValueMap, there is the possibility not only to show the values of the current layer but also the possible values in the referenced layer / configured possibilities.
age is a ValueMap, species is a ValueRelation and island_id is a RelationReference
In the example we have the persons: George (in Cuba, in his twenties, human) Paul (in Vietnam, in his thirties, human) Ringo (in Venezuela, in his forties, cat) John (in Vietnam as well, in his forties, table) And the entries in the country layer are USSR, Cuba, Vietnam, Burma, Venezuela, North Korea
This feature was developed by signedav