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In this chapter you will learn how to create accessible web pages following the standards of the World Wide Web Consortium.
Accessibility website of the Publications Office of the European Union: https://op.europa.eu/en/web/accessibi...

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All web-related data formats, protocols and guidelines are standardised by the World Wide Web Consortium (W3C).
The two core technologies defined for building web pages are the Hypertext Markup Language (HTML) and the Cascading Style Sheets (CSS). HTML provides the structure of a web page and CSS the layout.
The W3C working group Web Accessibility Initiative (WAI) has published the following standards:
The Web Content Accessibility Guidelines (WCAG), version 2.1.
The Accessible Rich Internet Applications (WAI-ARIA or ARIA), version 1.1.
The WCAG describe how to create accessible web content, and offer 13 guidelines following 4 principles:
1. Perceivable. Information and user-interface elements must be presented to users in a way they can perceive:
Provide text alternatives for non-text content, such as alternative descriptions for images.
Provide captions and other alternatives for multimedia, such as text transcripts, captions, sign language or audio descriptions.
Create content that can be presented in different ways, including by assistive technologies, without losing meaning.
Make it easier for users to see and hear content, for example by the selection of colours, choosing a sufficient contrast or having resizable text.
2. Operable. User-interface elements and navigation must be operable:
Make all functionality operable via a keyboard.
Give users enough time to read and use content.
Do not use content that causes seizures or physical reactions (animated or flashing content).
Help users to navigate and find content.
Make it easier to use input devices other than a keyboard.
3. Understandable. The information and the operation of the user interface must be understandable:
Make text readable and understandable.
Make content appear and operate in predictable ways. The navigation and user interface should be consistent.
Help users to avoid and correct mistakes by offering understandable error messages, correct form labelling and error prevention mechanisms.
4. Robust. Content must be robust enough so it can be interpreted by a wide variety of user agents, including assistive technologies.
Three levels of conformance are defined: A, AA and AAA. For example, to fulfil the level A, colour should not be used as the only means of conveying information. To achieve level AA, the visual presentation of text need to have a contrast ratio of at least 4.5 to 1. To reach the level AAA, the visual presentation of text has to have a contrast ratio of at least 7 to 1.
A website is considered to be compliant with a success criterion when all its web content fulfils the success criteria of the same level and all the levels below.
WCAG 2.0 can be applied to other file formats such as PDF, EPUB, Microsoft Word and Scalable Vector Graphics.
Today's web pages are more interactive, with drop-down menus, tabs, modal dialogue boxes, alert boxes, autocompletes and slideshows. These user interface controls are often not accessible to users with disabilities. This is where the ARIA standard comes in, allowing web pages to declare themselves as applications rather than as static documents, by adding role, property and state information.
Accessibility is not always visible! This makes it very difficult for people to understand the concepts of accessibility.
When looking at a web page, a sighted user immediately recognises different function blocks: banner, navigation, content, side box, footer and so on. They can also detect different headings, paragraphs, lists and tables. A user with visual disabilities does not have this information when facing a non-accessible web page.
A totally non-accessible web page has no structure. Therefore, all content has to be read in sequence. There are no possibilities to jump to the content part or a specific heading.
An accessible web page offers many different navigation features that enable the user to consume the content in multiple ways. A user with visual disabilities can get a quick overview of the structure of the web page before starting to read its content. Different lists showing landmarks, headings, forms, tables, links or images ease navigation significantly.
The number of navigation options increase with the level of accessibility.
A user may read the elements of a web page in sequence.
A user may navigate from heading to heading. The heading should start at level 1 and should be correctly nested.
A user may navigate from block to block with landmark roles, such as banner, navigation, main content or footer.
A user may navigate using links, images, tables or lists.