Understanding accessibility principles - Introduction

There are four principles in the Web Content Accessibility Guidelines (WCAG) which lay the foundation for anyone accessing and using web content. In this edition we give a broad outline of each, and will provide more specific detail and examples in forthcoming newsletters. Understanding each principle allows us to publish web content that reaches everyone visiting our site.


Users must be able to perceive the information being presented (it can't be invisible to all of their senses)

  • 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.
  • Time-based media: Provide alternatives for time-based media.
  • Create content that can be presented in different ways (for example simpler layout) without losing information or structure.
  • Make it easier for users to see and hear content including separating foreground from background.


Users must be able to operate the interface (the interface cannot require interaction that a user cannot perform)

  • Keyboard accessible: Make all functionality available from a keyboard.
  • Provide users enough time to read and use content.


Users must be able to understand the information as well as the operation of the user interface (the content or operation cannot be beyond their understanding)

  • Make text content readable and understandable.
  • Make web pages appear and operate in predictable ways.
  • Help users avoid and correct mistakes.


Content must be robust enough that it can be interpreted reliably by a wide variety of user agents, including assistive technologies. Users must be able to access the content even as technologies and user agents evolve.