Doctrine Of Pith And Substance

During the Judgment of Madras High Court, in matter of power tussle between the Lieutenant Governor and the Chief Minister of Puducherry, ‘Doctrine of Pith and Substance’ finds mention. What does this doctrine mean?

A
Union Government & State Government shall work in isolation.
B
Election to Union & State shall happen at the same time.
C
It defines the power of Lieutenant Governor.
D
Union & State Government shall not encroach in each other’s space.