# HTML content categories
HTML elements are grouped into content categories based on their function. These categories are important for understanding what constitutes valid markup in HTML. We'll see some examples of this in the next lecture when we talk about nesting HTML elements.
Some categories are subsets of other categories. For example, all elements which fall into the phrasing content category also fall into the flow content category.
We're not going to cover all of the HTML categories here, but there are a few that we should know about.
Note
Not all HTML elements have a content category. A notable example is the <html> element which surrounds all of our HTML markup.
# Flow content
Elements which fall into the flow content category generally contain text or embedded content such as images or videos.
Almost all HTML elements fall into this category, and every other category we're going to discuss in this section is a special subset of flow content.
Common elements which don't fall within these special subcategories include <div> elements, which are used as generic grouping elements, and <form> elements.
Text
Note that plain text is also considered flow content in HTML.
If the text contains more than just whitespace characters, it's also considered phrasing content. This is to distinguish the spaces used for indentation from actual text content.
You can find a complete list of flow content element here (opens new window).
# Sectioning content
Sectioning content includes special container elements used for grouping other elements into meaningful collections. This category includes elements like <article>, <section> and <nav>.
We're going to talk about each of these elements in detail later in this section, as you're going to be using them a lot!
Notable exceptions
One thing to note is that the <header>, <main>, and <footer> elements are not considered sectioning content. Instead, they're considered flow content.
You can find a complete list of sectioning content element here (opens new window).
# Heading content
The heading content category is reserved for the six heading elements in the HTML specification. These heading elements represent six levels of heading, and are numerically ordered from 1-6.
The most prominent of these headings is the <h1> element, which is usually reserved for something like a page title.
All heading elements can only contain phrasing content.
# Phrasing Content
For the most part, phrasing content represents the text of the document and the elements which mark up that text. However, phrasing content also includes some unexpected elements: <img>, <audio>, <video>, and others. This is because these elements revert to being plain text if the relevant resource can't be retrieved.
All elements which accept phrasing content are expected to have a descendent which contains some amount of plain text, and this is expected to contain content other than whitespace.
You can find a complete list of phrasing content element here (opens new window).