The book says 3♥/♠ shows weak 7-suit with <8 HCP. It gives an example for 3♠: ♠ Q1098432 ♥ 94 ♦ Q3 ♣ J4. Since slam chance is small, opener usually bids game (stop) or new suit (forcing). For example, after 2♣-3♥: 1) ♠ AK83 ♥ A ♦ AQ83 ♣ KQJ2 2) ♠ AKQJ842 ♥ - ♦ QJ1092 ♣ A With 1), bid 4♥; with 2), bid 3♠. With 8+ HCP and a major with two of AKQ, it suggests 2♥/♠.