I think they did mean nonscalar keys. Say I have a compoubd primary key in a database, over 3 columns. In YAML, representing that key as an array of the three c

I think they did mean nonscalar keys. Say I have a compoubd primary key in a database, over 3 columns. In YAML, representing that key as an array of the three columns' values (or a map from column name to value) makes sense, and so does using that as a key in other maps.