By agreement this showed a maximum pass with exactly three-card support for spades.

The jump to three spades suggested three-card support and about 11 points, so South might well have passed.

North has shown three-card support for South's heart suit.

Traditionally, this simply shows a strong hand, but the modern interpretation is three-card support for responder's suit.

North was able to show three-card support at his second turn, and South retreated to three no-trump.

North was able to give a jump preference to three diamonds, indicating three-card support with extra values.

With three-card support East would give strong, jump preference.

East raised her partner's three-spade opening to game, almost always the right move with three-card support regardless of strength.

The modern idea is to use it to show exactly three-card support for partner's suit.

This is a sensible way to bid holding three-card support for partner in a balanced hand with game values.