code: function(node, frame) {
                  var children = node.children;
                  for (var i = 0, l = children.length; i < l; i++) {
                      // TemplateData is a special case because it is never
                      // autoescaped, so simply output it for optimization
                      // ... 原字符串部分
                      if (children[i] instanceof nodes.TemplateData) {
                          if (children[i].value) {
                              this.emit(this.buffer + ' += ');
                              this.compileLiteral(children[i], frame);
                              this.emitLine(';');
                          }
                      } 
                      // ... 变量值
                      else {
                          // ...? 这是取变量的方法吗
                          this.emit(this.buffer + ' += runtime.suppressValue(');
                          this.compile(children[i], frame);
                          this.emit(', env.autoesc);\n');
                      }
                  }
              }
docs: ... 编译字符串的值 和 变量的值