Good question!

When we want to access to one of our constants, lets say ESTADO_USUARIO_ADMIN, we have three options:

- `Usuario:: ESTADO_USUARIO_ADMIN` will couple our engine with the app: our engine won't work unless the main app has a Usuario model
- `Kpi::UsuarioKpi:: ESTADO_USUARIO_ADMIN` will prevent the main app to overwrite the engine's defaults; we will keep using the engine's values, no matter what the main app says.
-`::Kpi::Clases.usuario_extern.constantize::ESTADO_USUARIO_ADMIN` will allow the main app to work with either Usuario or User, and will allow the main app overwrite the engine's default values. That's why I did this.