A token (in Dutch: kenmerk) is an identification relating a single respondent to a single survey instance for a single round in a track assigned to that respondent.
Tokens have valid from and optional valid until dates that define the period in which that survey can be answered for that respondent. These dates can be edited manually through the interface, but are usually determined by calculation rules set for the token's round in the track editor, specifying the valid from date e.g. through a date answer to an earlier survey in the track or through the valid from or until date of an earlier token or using some other date.
Once a token from or until date has been edited manually it will keep that value until another user removes that value - and then it is recalculated.