How does Vertica generate columns such as all_roles ?

Looking at the underlying definition for v_catalog.users, there are a few columns such as all_roles, default_roles, and search_path which generate a concatenated list of their respective data.

I was unable to find these columns in vs_columns which leads me to the question of how are these columns generated since there's no native group concatenation functionality?

I'm aware of Concatenate.cpp.