code: public function handle(Context $context)
      {
          $string = new StringExpr();
          $string->handle($context);
          $this->key = $string->getResult();
          
          $nameSeparator = new StructuralChar(array(":"));
          $nameSeparator->handle($context);
          
          $value = new Value();
          $value->handle($context);
          $this->value = $value->getResult();
      }
docs: 現在の Context から member 部分を読み込みます.
  
  @param Context $context