Cut cabbage into pieces that will fit into your food processor tube.
While motor is running put cabbage pieces into food processor; chop cabbage to make about 1 L (4 cups). Scrape into large bowl. Add carrots, celery, red pepper and parsley.
In small bowl, whisk together vinegar, oil, sugar, garlic, mustard, celery seed and pepper. Pour over cabbage mixture and toss to coat.
Storage: cover and refrigerate for up to 2 days.
Creamy variation: Stir in 1/4 cup light mayonnaise into the dressing and stir into slaw.