HTML title 全局属性

<p>
  Use the <code>title</code> attribute on an <code>iframe</code> to clearly
  identify the content of the <code>iframe</code> to screen readers.
</p>

<iframe
  title="Wikipedia page for the HTML language"
  src="https://en.m.wikipedia.org/wiki/HTML"></iframe>
<iframe
  title="Wikipedia page for the CSS language"
  src="https://en.m.wikipedia.org/wiki/CSS"></iframe>

iframe {
  height: 200px;
  margin-bottom: 24px;
  width: 100%;
}

<p>
  Newlines in <code>title</code> should be taken into account. This
  <span
    title="This is a
multiline title">
    example span
  </span>
  has a title a attribute with a newline.
</p>
<hr />
<pre id="output"></pre>

const span = document.querySelector("span");
const output = document.querySelector("#output");
output.textContent = span.title;

<div title="CoolTip">
  <p>Hovering here will show "CoolTip".</p>
  <p title="">Hovering here will show nothing.</p>
</div>