HTML guides

This page lists the guides for using HTML.

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. It's possible for elements (such as track) to not be a member of any of these categories.

Understanding quirks and standards modes

In the old days of the web, pages were typically written in two versions: One for Netscape Navigator, and one for Microsoft Internet Explorer. When the web standards were made at W3C, browsers could not just start using them, as doing so would break most existing sites on the web. Browsers therefore introduced two modes to treat new standards compliant sites differently from old legacy sites.

Using date and time formats in HTML

Certain HTML elements use date and/or time values. The formats of the strings that specify these values are described in this article.

Using HTML comments

An HTML comment is used to add explanatory notes to the markup or to prevent the browser from interpreting specific parts of the document.

Using HTML form validation and the Constraint Validation API

The creation of web forms has always been a complex task. While marking up the form itself is easy, checking whether each field has a valid and coherent value is more difficult, and informing the user about the problem may become a headache. HTML5 introduced new mechanisms for forms: it added new semantic types for the input element and constraint validation to ease the work of checking the form content on the client side. Basic, usual constraints can be checked, without the need for JavaScript, by setting new attributes; more complex constraints can be tested using the Constraint Validation API.

Using microdata in HTML

Microdata is part of the WHATWG HTML Standard and is used to nest metadata within existing content on web pages. Search engines and web crawlers can extract and process microdata from a web page and use it to provide a richer browsing experience for users. Search engines benefit greatly from direct access to this structured data because it allows search engines to understand the information on web pages and provide more relevant results to users. Microdata uses a supporting vocabulary to describe an item and name-value pairs to assign values to its properties. Microdata is an attempt to provide a declarative way of annotating HTML elements with machine-readable tags than the similar approaches of using RDFa and classic microformats.

Using microformats in HTML

Microformats are standards used to embed semantics and structured data in HTML, and provide an API to be used by social web applications, search engines, aggregators, and other tools. These minimal patterns of HTML are used for marking up entities that range from fundamental to domain-specific information, such as people, organizations, events, and locations.

Using responsive images in HTML

In this article, we'll learn about the concept of responsive images — images that work well on devices with widely differing screen sizes, resolutions, and other such features — and look at what tools HTML provides to help implement them. This helps to improve performance across different devices.

Using the viewport meta element

This article describes how to use the "viewport" <meta> tag to control the viewport's size and shape.