code: public Period and(float count, TimeUnit unit) {
      checkCount(count);
      return setTimeUnitValue(unit, count);
    }
docs: Set the given unit to have the given count.  Marks the
  unit as having been set.  This can be used to set
  multiple units, or to reset a unit to have a new count.
  This does <b>not</b> add the count to an existing count
  for this unit.
  
  @param count the number of units.  must be non-negative
  @param unit the unit
  @return the new Period