HTML列表訂購與無序解釋

有序列表（

<ol>）用於順序重要的內容，如步驟或排名，默認用數字標記；無序列表（ <ul>）用於順序無關的內容，如配料或標籤，默認用項目符號標記；1. 當順序重要時使用 <ol>；2. 當順序不重要時使用 <ul>；3. 兩者均可嵌套使用；選擇正確的列表類型有助於提升可訪問性和SEO。

When building web pages with HTML, lists are a fundamental way to organize content. There are two main types: ordered lists and unordered lists . They serve different purposes and are used depending on whether the sequence of items matters.

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What is an Ordered List?

An ordered list ( <ol></ol> ) is used when the order of the items is important. This type of list is typically displayed with numbers (1, 2, 3, etc.), though other numbering styles like letters (A, B, C) or Roman numerals (I, II, III) can be used via CSS.

Example:

 <ol>
  <li>Preheat the oven</li>
  <li>Mix the ingredients</li>
  <li>Bake for 30 minutes</li>
</ol>

This would display as:

<ol>

Preheat the oven

Mix the ingredients

Bake for 30 minutes

Because the steps must be followed in sequence, an ordered list makes sense here.

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What is an Unordered List?

An unordered list ( <ul> ) is used when the order doesn't matter. These are usually displayed with bullet points (like dots, dashes, or squares).

Example:

 <ul>
  <li>Flour</li>
  <li>Sugar</li>
  <li>Eggs</li>
</ul>

This would show as a simple bulleted list:

<ul>

Flour

Sugar

Eggs

Since the ingredients don't need to be listed in a specific order, an unordered list is appropriate.

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Key Differences at a Glance

Feature	Ordered List ( <ol> )	Unordered List ( <ul> )
Purpose	Sequence matters	Order doesn't matter
Default marker	Numbers	Bullets (discs)
Use case	Steps, rankings, instructions	Ingredients, features, tags
Nesting allowed	Yes (can mix with <ul> )	Yes (can mix with <ol> )

You can even nest lists inside each other. For example, a step in an ordered list might have sub-items that don't need ordering:

 <ol>
  <li>Prepare ingredients
    <ul>
      <li>Chop onions</li>
      <li>Grate cheese</li>
    </ul>
  </li>
  <li>Cook the dish</li>
</ol>

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When to Use Which?

<ul>

Use <ol></ol> when:

<ul>

Giving step-by-step instructions

Showing a ranking (eg, top 10 movies)

Presenting a timeline or process

Use <ul> when:

<ul>

Listing features of a product

Showing navigation menu items

Displaying tags, categories, or ingredients

Choosing the right list type improves not only the visual layout but also accessibility and SEO, since screen readers and search engines use these semantic elements to understand content structure.

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Basically, think: Does order matter?
→ Yes → <ol></ol>
→ No → <ul>

That's the core idea. Everything else—styling, nesting, accessibility—builds on that simple rule.

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