KUALA LUMPUR, April 19 -- A rare constitutional and adat dispute in Negeri Sembilan has thrust the state's unique traditional system into the national spotlight.

At the centre of the controversy are the Undang Yang Empat, or the four ruling chiefs whose roles, powers and selection processes differ significantly from the royal systems in other Malaysian states.

Here is a breakdown of who they are, how the system works, and why it matters in the current crisis.

What are the Undang?

Negeri Sembilan is the only state in Malaysia that practices Adat Perpatih, a Minangkabau-derived system rooted in matrilineal customs.

Under this system, the state is divided into traditional territories known as luak. Four of these are considered primary:...