An opening of two diamonds shows
(b) at least 5 hearts OR alternative a strong hand (minimum of 16 HCP, but usually partnerships play it to show 19+)
Response 2H -- additional rebids by opener shows a strong hand.
Playing Precision make 2H the limited short diamond hand and play 2D as a weak 2H or strong in any three suits. Presumably one rebids the singleton or suit below if not passing 2H
2D as a weak 2H or strong Flannery with 5 spades and 4 hearts. This frees 2H for standard Flannery