The "/tkthistory" page:

Show the complete change history for a single ticket. Or (to put it another way) show a list of artifacts associated with a single ticket.

By default, the artifacts are decoded and formatted. Text fields are formatted as text/plain, since in the general case Fossil does not have knowledge of the encoding. If the "raw" query parameter is present, then the undecoded and unformatted text of each artifact is displayed.