code: function isOTag (str, oTag, index) {
      var l = oTag.length, s = str.substr(index, l), sign = str.charAt(index+l);
      // NOTE 要保证sign有值 如果当前的index已经是字符串尾部 如'foo{{' sign为空
      if (oTag === s && sign && SIGN.indexOf(sign) > -1) {
          return {
              str: s + sign,
              index: index,
              // sign: signType[str.charAt(index+l)], // TODO: delete
              sign: str.charAt(index+l),
              // ignore the last oTag charts and the sign char,
              // l(oTag.length) - 1(oTag's first char) + 1(sign's char)
              jump: l
          };
      }
  }
docs: Is it the first char of an opening tag?