In a small bowl, whisk vinegar, lemon juice, mustard, 1/4 tsp. salt and 1/8 tsp. pepper. Keep whisking while adding oil in a slow stream. Dressing will thicken.
Combine cabbage, onion and carrots in a large bowl. Sprinkle caraway seeds over slaw and add dressing. Toss well and season with salt and pepper.
Cover and chill for at least 2 hours before serving.
