Format of participant, study, and session IDs for database schemata

I have an existing, mostly JavaScript-based experiment program that I think I’ll soon be modifying to run with Prolific. I wanted to ask, for the purpose of setting my database schema, what format can I expect PROLIFIC_PID, STUDY_ID, and SESSION_ID to be in? The example given in the documentation is, which suggests that the PID at least is always an integer in hexadecimal, but I don’t want to assume.