The main documentation of the Valid_State_Status Procedure contains additional explanation of this code listing.
function Valid_State_Status (S) result(Valid) ! Input variable. type(Status_type), intent(in) :: S ! Status to be checked. ! Output variable. type(logical) :: Valid ! Logical state. !~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ! Start out true. Valid = .true. ! Make sure the status variable is in range. Valid = Valid .and. S%status <= NFlags Valid = Valid .and. S%status >= 1 return end function Valid_State_Status