Reserved keys within pendo's meta data

Hey everyone! Within the pendo init script I noticed this line  You can add any additional visitor level key-values here, as long as it's not one of the above reserved names.

What exactly does this mean? Are id, email, full_name, and role all pre defined by pendo? 

                      // Call this whenever information about your visitors becomes available
                      // Please use Strings, Numbers, or Bools for value types.
                      pendo.initialize({
                          visitor: {
                              id:              'VISITOR-UNIQUE-ID'   // Required if user is logged in
                              // email:        // Recommended if using Pendo Feedback, or NPS Email
                              // full_name:    // Recommended if using Pendo Feedback
                              // role:         // Optional

                              // You can add any additional visitor level key-values here,
                              // as long as it's not one of the above reserved names.
                          },