<u>
Chinese proper names (and almost nothing else)
<u> — Semantic underline
The <u> element represents a segment of text carrying a non-textual annotation — typically an underline. In modern HTML, it is not meant for underlining text for style. Its legitimate use is limited.
When to use it
The only common use case: marking Chinese proper names (专名号). In Chinese typography, proper names are underlined to distinguish them from running text. Outside this case, avoid <u>. To emphasize a word, use <em>. To flag a spelling error, <u> with an appropriate role and style works — but <mark> or a CSS class is often preferable.
Never use <u> to underline a link or generic text. Underlines are reserved for links in web conventions — using them otherwise creates confusion.
What you gain
Accessibility: screen readers do not announce <u> differently from normal text. If the annotation has meaning, add a title attribute or visible context. The visual underline can be confused with a link by users with low vision.
Code example
<p lang="zh">
This novel was written by <u>曹雪芹</u>.
</p>