Collante is a further 'optional extra'. 

For example, after a 1♣ opening, the double of an intervening 1♦ promises a 4-card ♥ suit and the double of an intervening 1♥ promises a 4-card ♠ suit (7+ HCP). 

A direct response in a major thus promises a suit of at least 5 cards.

*Collante also functions similarly at the 2-level. The double of an intervening 2♦ promises a 4-card ♥ suit and the double of an intervening 2♥ promises a 4-card ♠ suit.

♣ ♦ ♥ ♠