docs: private static List<Integer> parseStep(String value, ValueParser parser) {
  		final List<String> parts = StrUtil.split(value, StrUtil.C_SLASH);
  		int size = parts.size();
  		
  		List<Integer> results;
  		if (size == 1) {// 普通形式
  			results = parseRange(value, -1, parser);
  		} else if (size == 2) {// 间隔形式
  			final int step = parser.parse(parts.get(1));
  			if (step < 1) {
  				throw new CronException("Non positive divisor for field: [{}]", value);
  			}
  			results = parseRange(parts.get(0), step, parser);
  		} else {
  			throw new CronException("Invalid syntax of field: [{}]", value);
  		}
  		return results;
  	}