code: function (token) {
              if (token.prev.type !== 'WhiteSpace') {
                  insertBefore(token, whiteSpaceFactory());
              }
              if (token.next.type !== 'WhiteSpace' && token.next.type !== 'LineBreak') {
                  insertAfter(token, whiteSpaceFactory());
              }
          }
docs: 保证一个token两侧是空白符
  
  @param {Object} token - target token