src/vs/editor/contrib/snippet/snippetParser.ts/Placeholder/compareByIndex
class Placeholder:	static compareByIndex(a: Placeholder, b: Placeholder): number {
		if (a.index === b.index) {
			return 0;
		} else if (a.isFinalTabstop) {
			return 1;
		} else if (b.isFinalTabstop) {
			return -1;
		} else if (a.index < b.index) {
			return -1;
		} else if (a.index > b.index) {
			return 1;
		} else {
			return 0;
		}
	}