全局HTML屬性適用於所有元素，用於改變行為或提供額外信息。 class用於CSS樣式和JS選擇；id為唯一標識符；style實現(xiàn)內(nèi)聯(lián)樣式；data-*存儲自定義數(shù)據(jù)；title顯示工具提示。這些屬性在網(wǎng)頁開發(fā)中非常實用且廣泛使用。

Global HTML attributes are special properties you can add to any HTML element to change its behavior or provide extra information. They aren't limited to specific tags — they work across all elements, making them super handy for general customization and functionality.

Here are some of the most commonly used global attributes and what they do:

class – For Styling and Selecting Elements

The class attribute lets you assign one or more class names to an element. These classes can then be used in CSS to style multiple elements at once or in JavaScript to target specific groups of elements.

Example:

 <p class="highlight">This paragraph has a highlight style applied.</p>

You can apply the same class to <div> , <span> , <button> , etc., and control their appearance from a single CSS rule.

Tips:

• Use meaningful names like btn-primary instead of generic ones like blue .
• You can use multiple classes by separating them with spaces: class="btn large primary" .

id – A Unique Identifier

Each HTML element can have an id attribute, which must be unique within the page. It's useful when you want to target a specific element with CSS or JavaScript.

Example:

• <div id="main-content">...</div>
• Then in CSS: #main-content { width: 100%; }

Important:

• Don't reuse the same ID on multiple elements — it breaks expected behavior.
• IDs are often used as anchor links: <a href="#section2">Go to Section 2</a>

style – Inline Styling

If you need to apply styles directly to a single element (not ideal for large sites), use the style attribute. This lets you write CSS rules right inside the HTML tag.

Example:

 <h1   style="max-width:90%">Big Red Heading</h1>

Keep in mind:

• It's best used sparingly — inline styles are hard to maintain.
• They override external and internal CSS unless marked with !important .

data-* Attributes – Store Custom Data

These are custom attributes that let you store extra info on an element. The * is a placeholder for any name you choose, like data-user-id or data-role .

Example:

 <button data-product-id="123" class="add-to-cart">Add to Cart</button>

Use cases:

• Used heavily in JavaScript to pass data between HTML and scripts.
• Avoid using these for things that belong in regular attributes or content.

title – Show Tooltips

When you hover over an element with a title attribute, a small tooltip appears. It's helpful for giving users quick hints without clicking.

Example:

 <a href="#" title="Visit our help center">Need help?</a>

Note:

• Works on almost any element, but most common on links and buttons.
• Not great for critical info — tooltips are easy to miss and not always accessible.

There are more global attributes like tabindex , contenteditable , and hidden , but those are used in more specific situations. Knowing the ones above will cover most day-to-day needs.

基本上就這些常用的全局HTML屬性，雖然簡單但很實用。

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