Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...a6/4. Ba4/4...Nf6/5. O-O/5...Be7/6. Re1/6...b5/7. Bb3/7...O-O/8. c3/8...d5/9. exd5/9...Nxd5/10. Nxe5/10...Nxe5/11. Rxe5/11...c6

Ruy Lopez, Marshall Gambit Main Line
Black's move ...c6 nails down the d5-knight. For White to chop it off (12. Bxd5) would now leave Black with the bishop pair on an open board, and three queenside pawns that would tightly restrain White's four.
 * 12. d4 is a natural developing move and the main line. Skip ahead to the first major fork in the road, which occurs after
 * 12...Bd6 13. Re1 Qh4 14. g3 Qh3
 * 12. d3 is a significant sideline favoured by Alexey Shirov. The pawn itself will be weaker for being on d3 instead of d4, but in return White gains the possibility of quickly converting the extra pawn into a passed pawn with a later c4 push. 12. d3 scores slightly better than 12. d4 at master level and is significantly less analysed.