Obstructing the opponent's queenside expansion well in advance with a novelty.
1. c2c4  1... g8f6  2. b1c3  2... e7e5  3. g1f3  3... b8c6  4. g2g3  4... c6d4 A relatively rare line, which Caruana also used some time ago. It seems as it is coming back into fashion these days at the top level. 5. f1g2  5... d4f3  6. g2f3  6... f8c5 The second main move. 7. d2d3 The main move is 7.0-0. 7... e8g8  8. e1g1 