Principles of Web Accessibility

The Web Content Accessibility Guidelines (WCAG) are the world standard for web accessibility. These guidelines are built upon four main principles of web accessibility:

  1. Perceivable,
  2. Operable,
  3. Understandable, and
  4. Robust

WCAG mandate that a website should conform to the four POUR principles in order to achieve full accessibility. These principles are essentially categories which contain relevant guidelines and checkpoints.

1. Perceivable

This principle states that the "information and user interface components must be presentable to users in ways they can perceive." It means that the user must be able to perceive/comprehend all the information presented on the website. All the information must be perceivable by the user through at least one of the senses.

Guidelines under the Perceivable Principle

  1. Text Alternatives: Provide text alternatives for any non-text content so that it can be changed into other forms people need, such as large print, braille, speech, symbols or simpler language.
  2. Time-based Media: Provide alternatives for time-based media.
  3. Adaptable: Create content that can be presented in different ways (for example simpler layout) without losing information or structure.
  4. Distinguishable: Make it easier for users to see and hear content including separating foreground from background.

2. Operable

This principle states that the "user interface components and navigation must be operable." In simple words, it means that every user must be able to operate all the parts of the web interface. No part of the interface should require an action that the user can not perform.

Guidelines under the Operable Principle

  1. Keyboard Accessible: Make all functionality available from a keyboard.
  2. Enough Time: Provide users enough time to read and use content.
  3. Seizures and Physical Reactions: Do not design content in a way that is known to cause seizures or physical reactions.
  4. Navigable: Provide ways to help users navigate, find content, and determine where they are.
  5. Input Modalities: Make it easier for users to operate functionality through various inputs beyond keyboard.

3. Understandable

This principle states that the "information and the operation of user interface must be understandable."

Guidelines under the Understandable Principle

  1. Readable: Make text content readable and understandable.
  2. Predictable: Make Web pages appear and operate in predictable ways.
  3. Input Assistance: Help users avoid and correct mistakes.

4. Robust

This principle states that the content must be robust enough that it can be interpreted by by a wide variety of user agents, including assistive technologies. The accessibility of the website must be such that it remain effective across various platforms and technologies.

Guidelines under the Robust Principle

  1. Compatible: Maximize compatibility with current and future user agents, including assistive technologies.