code: function (val) {
              if (val === undefined || val === null) {
                  return '';
              }
              //接收到的是raw包装的字符串，则不转义。If get an object with 'raw' property, no encode.
              if (val.$saker_raw$) {
                  return val.str;
              }
              if (typeof val !== 'string') {
                  return val;
              }
              var map = {
                  '&': '&amp;',
                  '<': '&lt;',
                  '>': '&gt;',
                  '"': '&quot;',
                  "'": '&#039;'
              };
  
              return val.replace(/[&<>"']/g, function (m) {
                  return map[m];
              });
          }
docs: 转义特殊字符。Encode special characters.
  @param val
  @returns {XML|string|void|*}