code: function () {
              var len = this.source.length,
                  char,
                  matched,
                  result = '';
              if (this.position >= len) {
                  return undefined;
              }
              for (; this.position < len; this.position++) {
                  char = this.readNextChars(1);
                  //读到 '@' 就停止，因为 '@' 后面的必定是脚本代码。Stop if '@', for the code behind '@' must be the server scripts.
                  if (char === configure.symbol) {
                      break;
                  }
  
                  if (char === '<' && /^<(\w+)/.test(this.readNextChars(50))) {
                      matched = this.readNextChars(50).match(/^<(\w+)/);
                      this.tags.push({
                          type: matched[1],
                          position: this.position
                      });
                  }
  
                  //遇到 > 并且之前已经遇到过开始标签了。Meet '>' and there exists start tag.
                  if (char === '>' && this.tags.length > 0) {
                      //...</div> , <img >
                      if (new RegExp('<(\\\\)?\/' + this.tags[this.tags.length - 1].type + '\\s*>$').test(this.readPrevChars() + char) || this.selfClosedTags.indexOf(this.tags[this.tags.length - 1].type) > -1) {
                          this.tags.pop();
                          result += char;
                          if ((this.tags[this.tags.length - 1] || {position: -1}).position >= (this.braces[this.braces.length - 1] || {position: -1}).position) {
                              continue;
                          } else {
                              this.position += 1;
                              //如果接下来的字符是空格。If next char is whitespace.
                              if (this.readNextChars(1).match(/\s/)) {
                                  result += this.readNextChars(1);
                                  this.position += 1;
                              }
                              break;
                          }
                      }
                  }
  
                  result += char;
              }
  
              //准备进入后端读取模式。Ready to switch to backend read mode.
              this.state = stateEnum.server;
              return result;
          }
docs: 读取前端标记代码。Read client markup.
  @returns {*}