I was reading through the Public Network Terms of Service. What does the following passage refer to?
- Some premium or additional features of Stack Overflow (including without limitation Stack Overflow for Teams) may require a payment obligation for access and use. You are solely responsible for ensuring that your payment obligations, if any, remain current and not in arrears. In the event Stack Overflow charges for features you will be clearly notified of the terms of any payment obligations and provided the opportunity to refuse such obligations before you incur any charges. Please note, however, that your refusal to accept payment obligations may result in your inability to access or use certain premium or additional features of Stack Overflow.
What "premium or additional features" exactly cost money?