code: public function parse($value, $rule)
      {
          $rs = $value;
  
          $ruleFormat = !empty($rule['format']) ? strtolower($rule['format']) : '';
          if ($ruleFormat == 'timestamp') {
              $rs = strtotime($value);
              if ($rs <= 0) {
                  $rs = 0;
              }
  
              $rs = $this->filterByRange($rs, $rule);
          }
  
          return $rs;
      }
docs: 对日期进行格式化
  
  @param int $value 变量值
  @param array $rule ['format' => 'timestamp', 'min' => '最小值', 'max' => '最大值']
  @return int|string 格式化后的变量