code: def visit(self):
          
          for enrollment in self._get_all_enrollments():
              if enrollment.experiment.is_displaying_alternatives():
                  # We have two different goals, VISIT_NOT_PRESENT_COUNT_GOAL and VISIT_PRESENT_COUNT_GOAL.
                  # VISIT_PRESENT_COUNT_GOAL will avoid firing on the first time we set last_seen as it is assumed that the user is
                  # on the page and therefore it would automatically trigger and be valueless.
                  # This should be used for experiments when we enroll the user as part of the pageview,
                  # alternatively we can use the NOT_PRESENT GOAL which will increment on the first pageview,
                  # this is mainly useful for notification actions when the users isn't initially present.
  
                  if not enrollment.last_seen:
                      self._experiment_goal(enrollment.experiment, enrollment.alternative, conf.VISIT_NOT_PRESENT_COUNT_GOAL, 1)
                      self._set_last_seen(enrollment.experiment, now())
                  elif now() - enrollment.last_seen >= timedelta(hours=conf.SESSION_LENGTH):
                      self._experiment_goal(enrollment.experiment, enrollment.alternative, conf.VISIT_NOT_PRESENT_COUNT_GOAL, 1)
                      self._experiment_goal(enrollment.experiment, enrollment.alternative, conf.VISIT_PRESENT_COUNT_GOAL, 1)
                      self._set_last_seen(enrollment.experiment, now())
docs: Record that the user has visited the site for the purposes of retention tracking