为什么将一个附加到动态创建的中似乎会在父页面中运行该脚本？

为什么将一个
$(function() {
  var test = '这个应该在里面吗？';
  $('body').append(test);
});
</pre>
<p></p>
<p>看起来不寻常的一件事是，甚至在<strong>iframe_test.js</strong>中的代码也能正常工作；我没有在<iframe>本身中加载jQuery，只在父文档中加载了jQuery。这对我来说似乎是一个线索，但我无法弄清楚它的含义。</p>
<p>任何想法、建议等都将不胜感激！</p>
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