在HTML5中，<em>和<i>雖然默認(rèn)都顯示為斜體，但語(yǔ)義和用途不同；1.<em>用於強(qiáng)調(diào)內(nèi)容，影響屏幕閱讀器的語(yǔ)調(diào)，適合突出重要信息；2.<i>用於樣式或語(yǔ)義上的區(qū)分，如技術(shù)術(shù)語(yǔ)、外來(lái)詞等，不增加語(yǔ)義權(quán)重；3.選擇合適標(biāo)籤有助於提升可訪問(wèn)性和SEO效果。

In HTML5, the <em></em> and <i></i> tags both display text in italics by default, but they serve different purposes when it comes to meaning and accessibility. The key difference is semantic: <em></em> is used for emphasis, while <i></i> is for text that's stylistically different but not more important.

<em></em> : Use It When You Want to <em>Emphasize Something

The <em></em> tag is meant to indicate emphasis. When you wrap text in <em></em> , you're telling browsers, screen readers, and search engines that this part of the sentence carries extra importance or emotion.

For example:

<p>I really hope you <em>remember</em> this part.</p>

In this case, "remember" is emphasized — like you're giving it a little verbal push when reading aloud.

• Screen readers may change tone slightly when reading <em> content.
• By default, browsers render <em> in italics, but you can override this with CSS if needed.
• It's good practice to use <em> when you want to stress a word or phrase within a sentence.

This makes <em> ideal for highlighting important points in your content from an accessibility standpoint.

<i> : For Stylistic or Semantic Alternation Without Emphasis

The <i> tag also makes text italic by default, but it doesn't carry the same weight as <em> . It's often used for technical terms, foreign words, thoughts, or ship names — things that are conventionally italicized but not necessarily emphasized.

Example:

<p>The term <i>deus ex machina</i> is often used in storytelling.</p>

Here, the Latin phrase is set apart stylistically, but there's no added emphasis or emotional weight.

• <i></i> should be used sparingly and only when there's a clear typographic or semantic reason.
• Avoid using <i></i> just to make text italic — better to use CSS ( font-style: italic ) for pure styling.
• Think of <i></i> as a way to mark up text that has a different tone or origin, not a stronger one.

It's especially useful in educational or literary contexts where certain phrases need visual distinction without altering their spoken tone for assistive technologies.

How They Affect Accessibility

One big reason to choose between <em></em> and <i></i> carefully is how assistive technologies interpret them.

• Screen readers will typically announce the presence of <em></em> , sometimes changing pitch or tone to reflect the emphasis.
• With <i></i> , there's usually no change in how the text is read — it's treated as normal text, even though it looks different visually.

So if you're aiming for inclusive design, choosing the right tag helps ensure that all users get the intended message — not just those who can see the italics.

Final Thoughts

Both <em></em> and <i></i> can produce italic text, but they do so with different intentions. Use <em></em> when you want to highlight something important or give it verbal weight. Reach for <i></i> when you need to follow a typographic convention without adding emphasis.

Semantics matter, especially for accessibility and SEO. So it's worth taking a second to ask yourself: do I want this text to <em>stand out , or to <em>stand apart ?

That's basically it.

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