Content categories

Most HTML elements are a member of one or more content categories — these categories group elements that share common characteristics. This is a loose grouping (it doesn't actually create a relationship among elements of these categories), but they help define and describe the categories' shared behavior and their associated rules, especially when you come upon their intricate details. It's also possible for elements to not be a member of any of these categories.

There are three types of content categories:

Main content categories, which describe common rules shared by many elements.
Form-related content categories, which describe rules common to form-related elements.
Specific content categories, which describe rare categories shared only by a few elements, sometimes only in a specific context.

Note: A more detailed discussion of these content categories and their comparative functionalities is beyond the scope of this article; for that, you may wish to read the relevant portions of the HTML specification.

A Venn diagram showing how the various content categories interrelate. The following sections explain these relationships in text.

Main content categories

Metadata content

Elements belonging to the metadata content category modify the presentation or the behavior of the rest of the document, set up links to other documents, or convey other out-of-band information. Everything in the <head>, including the <title>, <link>, <script>, <style>, and the lesser used <base>, is metadata content. There is a <meta> element for metadata that cannot be represented by these other elements.

The metadata elements are:

Some of these elements belong to more than one content category. For example, <script> is a member of the metadata, flow, and phrasing content categories, and is a script-supporting element; <script> can be used where metadata content, phrasing content, or script-supporting elements are expected.

Flow content

Flow content is a broad category that encompasses most elements that can go inside the <body> element, including heading elements, sectioning elements, phrasing elements, embedding elements, interactive elements, and form-related elements. It also includes text nodes (but not those that only consist of white space characters).

The flow elements are:

A few other elements belong to this category, but only if a specific condition is fulfilled:

<area>, if it is a descendant of a <map> element
<link>, if the itemprop attribute is present
<meta>, if the itemprop attribute is present

Sectioning content

Sectioning content, a subset of flow content, creates a section in the current outline defining the scope of <header> and <footer> elements.

The sectioning elements are:

Heading content

Heading content, a subset of flow content, defines the title of a section. This definition applies both to sections marked by an explicit sectioning content elements and to those implicitly defined by the heading content itself.

The heading elements are:

Note: Though likely to contain heading content, the <header> is not heading content itself.

Phrasing content

Phrasing content, a subset of flow content, refers to the text and the markup within a document. Sequences of phrasing content make up paragraphs.

The phrasing elements are:

<abbr>
<audio>
<b>
<bdi>
<bdo>
<br>
<button>
<canvas>
<cite>
<code>
<data>
<datalist>
<dfn>
<em>
<embed>
<i>
<iframe>
<img>
<input>
<kbd>
<label>
<mark>
<math>
<meter>
<noscript>
<object>
<output>
<picture>
<progress>
<q>
<ruby>
<s>
<samp>
<script>
<select>
<slot>
<small>
<span>
<strong>
<sub>
<sup>
<svg>
<template>
<textarea>
<time>
<u>
<var>
<video>
<wbr>
plain text (including more than just whitespace characters)

A few other elements belong to this category, but only if a specific condition is fulfilled:

<a>, if it contains only phrasing content
<area>, if it is a descendant of a <map> element
<del>, if it contains only phrasing content
<ins>, if it contains only phrasing content
<link>, if the itemprop attribute is present
<map>, if it contains only phrasing content
<meta>, if the itemprop attribute is present

Embedded content

Embedded content, a subset of flow content, imports another resource or inserts content from another markup language or namespace into the document.

The embedded content elements are:

Interactive content

Interactive content, a subset of flow content, includes elements that are specifically designed for user interaction.

The interactive content elements are:

Some elements belong to this category only under specific conditions:

<a>, if the href attribute is present
<audio>, if the controls attribute is present
<img>, if the usemap attribute is present
<input>, if the type attribute is not in the hidden state
<object>, if the usemap attribute is present
<video>, if the controls attribute is present

Palpable content

Content is palpable when it's neither empty nor hidden; it is content that is rendered and is substantive. Elements whose model is flow content should have at least one node which is palpable.

The palpable elements are:

<a>
<abbr>
<address>
<article>
<aside>
<b>
<bdi>
<bdo>
<blockquote>
<button>
<canvas>
<cite>
<code>
<data>
<del>
<details>
<dfn>
<div>
<em>
<embed>
<fieldset>
<footer>
<figure>
<form>
<iframe>
<img>
<ins>
<kbd>
<label>
<main>
<map>
<mark>
<math> from MathML
<meter>
<nav>
<object>
<p>
<picture>
<pre>
<progress>
<q>
<ruby>
<s>
<samp>
<search>
<section>
<select>
<small>
<span>
<strong>
<sub>
<sup>
<svg> from SVG
<table>
<textarea>
<time>
<u>
<var>
<video>
Autonomous custom elements
text that is not inter-element whitespace

Some elements belong to this category only under specific conditions:

<audio>, if the controls attribute is present
<dl>, if the element's children include at least one name-value group
<input>, if the type attribute is not in the hidden state
<ol>, if it's children include at least one <li> element
<ul>, if it's children include at least one <li> element

Form-associated content

Form-associated content is a subset of flow content comprising elements that have a form owner, exposed by a form attribute, and can be used everywhere flow content is expected. A form owner is either the containing <form> element or the element whose id is specified in the form attribute.

The form-associated elements are:

This category contains several sub-categories:

listed: Elements that are listed in the form.elements and fieldset.elements collections. Contains <button>, <fieldset>, <input>, <object>, <output>, <select>, and <textarea>.
labelable: Elements that can be associated with <label> elements. Contains <button>, <input>, <meter>, <output>, <progress>, <select>, and <textarea>.
submittable: Elements that can be used for constructing the form data set when the form is submitted. Contains <button>, <input>, <object>, <select>, and <textarea>.
resettable: Elements that can be affected when a form is reset. Contains <input>, <output>, <select>, and <textarea>.

Secondary content categories

There are some secondary classifications of elements that can be useful to be aware of as well.

Script-supporting elements

Script-supporting elements are elements that don't directly contribute to a document's rendered output. Instead, they serve to support scripts, either by containing or specifying script code directly or by specifying data that will be used by scripts.

The script-supporting elements are:

Transparent content model

If an element has a transparent content model, then its contents must be structured such that they would be valid HTML, even if the transparent element were removed and replaced by the child elements.

For example, the <del> and <ins> elements are transparent:

html

<p><del>Shopping</del> <ins>Returns</ins> list</p>
<ul>
  <del>
    <li>Oranges</li>
    <li>Toilet paper</li>
  </del>
  <li>Toothpaste</li>
</ul>

If those elements were removed, this fragment would still be valid HTML (if not correct English).

html

<p>Shopping Returns list</p>
<ul>
  <li>Oranges</li>
  <li>Toilet paper</li>
  <li>Toothpaste</li>
</ul>