<Tr> <Th> Relegated </Th> <Td> North Ferriby United Gainsborough Trinity Tamworth </Td> </Tr> <Tr> <Td_colspan="2"> ← 2016--17 2018--19 → </Td> </Tr> <Table> <Tr> <Td> To National League North (edit) <P> Promoted from Northern Premier League Premier Division </P> <Ul> <Li> Blyth Spartans </Li> <Li> Spennymoor Town </Li> </Ul> <P> Promoted from Southern Football League Premier Division </P> <Ul> <Li> Leamington </Li> </Ul> <P> Relegated from National League </P> <Ul> <Li> York City </Li> <Li> Southport </Li> <Li> North Ferriby United </Li> </Ul> </Td> <Td> From National League North (edit) <P> Relegated to Northern Premier League Premier Division </P> <Ul> <Li> Altrincham </Li> <Li> Stalybridge Celtic </Li> </Ul> <P> Relegated and voluntarily demoted to Midland Football League Premier Division </P> <Ul> <Li> Worcester City </Li> </Ul> <P> Transferred to National League South </P> <Ul> <Li> Gloucester City </Li> </Ul> <P> Promoted to National League </P> <Ul> <Li> Fylde </Li> <Li> Halifax Town </Li> </Ul> </Td> </Tr> </Table> <Tr> <Td> To National League North (edit) <P> Promoted from Northern Premier League Premier Division </P> <Ul> <Li> Blyth Spartans </Li> <Li> Spennymoor Town </Li> </Ul> <P> Promoted from Southern Football League Premier Division </P> <Ul> <Li> Leamington </Li> </Ul> <P> Relegated from National League </P> <Ul> <Li> York City </Li> <Li> Southport </Li> <Li> North Ferriby United </Li> </Ul> </Td> <Td> From National League North (edit) <P> Relegated to Northern Premier League Premier Division </P> <Ul> <Li> Altrincham </Li> <Li> Stalybridge Celtic </Li> </Ul> <P> Relegated and voluntarily demoted to Midland Football League Premier Division </P> <Ul> <Li> Worcester City </Li> </Ul> <P> Transferred to National League South </P> <Ul> <Li> Gloucester City </Li> </Ul> <P> Promoted to National League </P> <Ul> <Li> Fylde </Li> <Li> Halifax Town </Li> </Ul> </Td> </Tr>

How do the playoffs work in the national league