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Table of Contents
What is an HTML document outline?
How to correctly build an HTML document outline?
Common misunderstandings and precautions
How do tools help us check out the outline?
Home Web Front-end HTML Tutorial What is the HTML Document Outline?

What is the HTML Document Outline?

Jul 13, 2025 am 01:07 AM

HTML document outline is a content structure automatically constructed by the browser based on title tags and semantic tags. It is used to express the hierarchical relationship of page information and affect accessibility, SEO and browser behavior. Its core construction methods include: 1. Use titles in hierarchical order without skipping; 2. Used in conjunction with semantic tags, each block can have a title structure independently; 3. Avoid multiple h1s to improve compatibility and SEO. Common misunderstandings include title jumps, random nesting of h1s, and ignoring auxiliary technology needs. Outline issues can be checked through browser extensions, W3C verification tools, or screen readers. Reasonable organization of titles and semantic labels can effectively improve the clarity of document structure.

What is the HTML Document Outline?

The outline structure of an HTML document is defined by title tags ( <h1></h1> to <h6></h6> ) and semantic tags (such as <section></section> , <article></article> , <nav></nav> , etc.). It not only affects the hierarchical relationship of page content, but also has an important impact on accessibility, SEO, and browser default behavior.

What is the HTML Document Outline?

What is an HTML document outline?

Simply put, HTML document outline is a content structure that the browser automatically builds based on the title and semantic tags you use. It does not control styles like CSS, but helps browsers, screen readers and other tools to understand the levels and focus of page information. For example, a correct document outline can make it easier for visually impaired users to navigate the entire page content.

If you only use <h1></h1> to <h6></h6> to organize content, the outline mainly relies on the nested structure of these titles. After HTML5 introduces semantic tags, even if you use <h2></h2> in a <section></section> , the browser may treat it as the top title of the block.

What is the HTML Document Outline?

How to correctly build an HTML document outline?

To make the outline clear and reasonable, the key lies in the order of the title and the way the semantic elements are used .

  • Use titles by level : Do not skip the level and use titles. For example, in the main content area, use <h1></h1> first, then <h2></h2> , and then <h3></h3> , so that the logic is clear.
  • Used in conjunction with semantic tags : each <section></section> or <article></article> can have its own title structure, which is relatively independent of them. For example:
 <section>
  <h2>Introduction</h2>
  <p>This is the introduction. </p>
</section>
<section>
  <h2>Text</h2>
  <h3>Background</h3>
  <p>This is the background part of the text. </p>
</section>

In this way of writing, <h2></h2> in both <section></section> are equivalent to the "first-level title" of their respective areas and will not interfere with each other.

What is the HTML Document Outline?
  • Avoid multiple <h1></h1> : While HTML5 allows multiple <h1></h1> to be used in a single page, it is generally recommended to keep only one main title for compatibility and SEO considerations.

Common misunderstandings and precautions

Many people ignore the existence of the outline, resulting in structural confusion. Here are a few common questions:

  • ? Use title jumps, such as jumping directly from <h1></h1> <h3></h3>
  • ?Nest multiple <h1></h1> at will without semantic tag wrapping
  • ? Ignore the dependence of assistive technologies on the outline, such as screen reader users may jump quickly through the title

For example: If there are multiple <h1></h1> in a page without a semantic tag wrap, some screen readers may misjudgment which is the real main title, which will affect the user experience.


How do tools help us check out the outline?

Currently there are some tools that can help developers view and verify the outline structure of HTML documents:

  • Browser extensions such as "HeadingsMap" (Chrome)
  • W3C's online verification tool
  • The title navigation function (such as NVDA) comes with the screen reader

These tools can help you find out whether the title is duplicated, whether there are skipping grades, etc.


Basically that's it. As long as you pay attention to the title order and use semantic tags reasonably, you can build a clear and easy-to-read HTML document structure. This doesn't seem complicated, but it's easy to ignore.

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