
                  },
                  users: {
                    type: 'array',
                    items: {
                      type: 'object',
                      properties: {
                        firstname: {
                          type: 'string',
                          ui: {
                            columns: 4
                          },
                          rules: {
                            required: 'dx: {{$root.age}} > 18'
                          }
                    