WCAG 2.0: Understanding documents

Understanding WCAG 2.0

Updated 7 June 2023


Understanding WCAG 2.0 is a guide to understanding and using Web Content Accessibility Guidelines (WCAG) 2.0 [[WCAG20]]. It is part of a set of documents that support WCAG 2.0. Please note that the contents of this document are informative (they provide guidance), and not normative (they do not set requirements for conforming to WCAG 2.0). See Web Content Accessibility Guidelines (WCAG) Overview for an introduction to WCAG, supporting technical documents, and educational material.

Status of This Document

This is the official version of "Understanding WCAG 2.0", and is referenced by Web Content Accessibility Guidelines 2.0. This resource is maintained as needed to update interpretive guidance and reference techniques to meet the guidelines.

To comment, file an issue in the W3C WCAG GitHub repository. Although the proposed Success Criteria in this document reference issues tracking discussion, the Working Group requests that public comments be filed as new issues, one issue per discrete comment. It is free to create a GitHub account to file issues. If filing issues in GitHub is not feasible, send email to public-agwg-comments@w3.org (comment archive).


Understanding WCAG 2.0 is a guide to understanding and using Web Content Accessibility Guidelines 2.0 [[WCAG20]] Although the normative definition and requirements for WCAG 2.0 can all be found in the WCAG 2.0 document itself, the concepts and provisions may be new to some people. Understanding WCAG 2.0 provides a non-normative extended commentary on each guideline and each Success Criterion to help readers better understand the intent and how the guidelines and Success Criteria work together. It also provides examples of techniques or combinations of techniques that the Working Group has identified as being sufficient to meet each Success Criterion. Links are then provided to write-ups for each of the techniques.

Structure of Understanding WCAG 2.0

This is not an introductory document. It is a detailed technical description of the guidelines and their Success Criteria. See Web Content Accessibility Guidelines (WCAG) Overview for an introduction to WCAG, supporting technical documents, and educational material.

Understanding WCAG 2.0 is organized by guideline. There is an Understanding Guideline X.X section for each guideline. The intent and any advisory techniques that are related to the guideline but not specifically related to any of its Success Criteria are listed there as well.

The Understanding Guidelines X.X section is then followed by a Understanding Success Criterion X.X.X section for each Success Criterion of that guideline. These sections each contain:

Links are provided from each Guideline in WCAG 2.0 directly to each Understanding Guideline X.X in this document. Similarly, there is a link from each Success Criterion in WCAG 2.0 to the Understanding Success Criterion X.X.X section in this document.

Techniques for WCAG 2.0

Techniques specific to WCAG 2.0 are added to the the techniques for WCAG 2.0, it is one set. The Techniques change log lists the new techniques added since WCAG 2.0 was published.

All Understanding documents

Understanding Guidelines and Success Criteria


  1. 1.1 Text Alternatives
    1. 1.1.1 Non-text Content
  2. 1.2 Time-based Media
    1. 1.2.1 Audio-only and Video-only (Prerecorded)
    2. 1.2.2 Captions (Prerecorded)
    3. 1.2.3 Audio Description or Media Alternative (Prerecorded)
    4. 1.2.4 Captions (Live)
    5. 1.2.5 Audio Description (Prerecorded)
    6. 1.2.6 Sign Language (Prerecorded)
    7. 1.2.7 Extended Audio Description (Prerecorded)
    8. 1.2.8 Media Alternative (Prerecorded)
    9. 1.2.9 Audio-only (Live)
  3. 1.3 Adaptable
    1. 1.3.1 Info and Relationships
    2. 1.3.2 Meaningful Sequence
    3. 1.3.3 Sensory Characteristics
  4. 1.4 Distinguishable
    1. 1.4.1 Use of Color
    2. 1.4.2 Audio Control
    3. 1.4.3 Contrast (Minimum)
    4. 1.4.4 Resize text
    5. 1.4.5 Images of Text
    6. 1.4.6 Contrast (Enhanced)
    7. 1.4.7 Low or No Background Audio
    8. 1.4.8 Visual Presentation
    9. 1.4.9 Images of Text (No Exception)


  1. 2.1 Keyboard Accessible
    1. 2.1.1 Keyboard
    2. 2.1.2 No Keyboard Trap
    3. 2.1.3 Keyboard (No Exception)
  2. 2.2 Enough Time
    1. 2.2.1 Timing Adjustable
    2. 2.2.2 Pause, Stop, Hide
    3. 2.2.3 No Timing
    4. 2.2.4 Interruptions
    5. 2.2.5 Re-authenticating
  3. 2.3 Seizures and Physical Reactions
    1. 2.3.1 Three Flashes or Below Threshold
    2. 2.3.2 Three Flashes
  4. 2.4 Navigable
    1. 2.4.1 Bypass Blocks
    2. 2.4.2 Page Titled
    3. 2.4.3 Focus Order
    4. 2.4.4 Link Purpose (In Context)
    5. 2.4.5 Multiple Ways
    6. 2.4.6 Headings and Labels
    7. 2.4.7 Focus Visible
    8. 2.4.8 Location
    9. 2.4.9 Link Purpose (Link Only)
    10. 2.4.10 Section Headings


  1. 3.1 Readable
    1. 3.1.1 Language of Page
    2. 3.1.2 Language of Parts
    3. 3.1.3 Unusual Words
    4. 3.1.4 Abbreviations
    5. 3.1.5 Reading Level
    6. 3.1.6 Pronunciation
  2. 3.2 Predictable
    1. 3.2.1 On Focus
    2. 3.2.2 On Input
    3. 3.2.3 Consistent Navigation
    4. 3.2.4 Consistent Identification
    5. 3.2.5 Change on Request
  3. 3.3 Input Assistance
    1. 3.3.1 Error Identification
    2. 3.3.2 Labels or Instructions
    3. 3.3.3 Error Suggestion
    4. 3.3.4 Error Prevention (Legal, Financial, Data)
    5. 3.3.5 Help
    6. 3.3.6 Error Prevention (All)


  1. 4.1 Compatible
    1. 4.1.1 Parsing
    2. 4.1.2 Name, Role, Value

Other Understanding documents

Understanding documents change Log

A list of significantly updated Understanding documents since WCAG 2.0 was published:

  1. : Updated Understanding Non-text contrast, based on the changes from Pull request 550.

For a more detailed view of recent changes to the informative documents see the github updates.


Additional information about participation in the Accessibility Guidelines Working Group (AG WG) can be found on the Working Group home page.

Participants of the AG WG active in the development of this document:

Other previously active WCAG WG participants and other contributors to WCAG 2.0, WCAG 2.1, or supporting resources

Paul Adam, Jenae Andershonis, Wilhelm Joys Andersen, Andrew Arch, Avi Arditti, Aries Arditi, Mark Barratt, Mike Barta, Sandy Bartell, Kynn Bartlett, Chris Beer, Charles Belov, Marco Bertoni, Harvey Bingham, Chris Blouch, Paul Bohman, Frederick Boland, Denis Boudreau, Patrice Bourlon, Andy Brown, Dick Brown, Doyle Burnett, Raven Calais, Ben Caldwell, Tomas Caspers, Roberto Castaldo, Sofia Celic-Li, Sambhavi Chandrashekar, Mike Cherim, Jonathan Chetwynd, Wendy Chisholm, Alan Chuter, David M Clark, Joe Clark, Darcy Clarke, James Coltham, Earl Cousins, James Craig, Tom Croucher, Pierce Crowell, Nir Dagan, Daniel Dardailler, Geoff Deering, Sébastien Delorme, Pete DeVasto, Iyad Abu Doush, Sylvie Duchateau, Cherie Eckholm, Roberto Ellero, Don Evans, Gavin Evans, Neal Ewers, Steve Faulkner, Bengt Farre, Lainey Feingold, Wilco Fiers, Michel Fitos, Alan J. Flavell, Nikolaos Floratos, Kentarou Fukuda, Miguel Garcia, P.J. Gardner, Alistair Garrison, Greg Gay, Becky Gibson, Al Gilman, Kerstin Goldsmith, Michael Grade, Karl Groves, Loretta Guarino Reid, Jon Gunderson, Emmanuelle Gutiérrez y Restrepo, Brian Hardy, Eric Hansen, Benjamin Hawkes-Lewis, Sean Hayes, Shawn Henry, Hans Hillen, Donovan Hipke, Bjoern Hoehrmann, Allen Hoffman, Chris Hofstader, Yvette Hoitink, Martijn Houtepen, Carlos Iglesias, Richard Ishida, Jonas Jacek, Ian Jacobs, Phill Jenkins, Barry Johnson, Duff Johnson, Jyotsna Kaki, Shilpi Kapoor, Leonard R. Kasday, Kazuhito Kidachi, Ken Kipness, Johannes Koch, Marja-Riitta Koivunen, Preety Kumar, Kristjan Kure, Andrew LaHart, Gez Lemon, Chuck Letourneau, Aurélien Levy, Harry Loots, Scott Luebking, Tim Lacy, Jim Ley, Alex Li, William Loughborough, N Maffeo, Mark Magennis, Kapsi Maria, Luca Mascaro, Matt May, Sheena McCullagh, Liam McGee, Jens Oliver Meiert, Niqui Merret, Jonathan Metz, Alessandro Miele, Steven Miller, Mathew J Mirabella, Matt May, Marti McCuller, Sorcha Moore, Charles F. Munat, Robert Neff, Charles Nevile, Liddy Nevile, Dylan Nicholson, Bruno von Niman, Tim Noonan, Sebastiano Nutarelli, Graham Oliver, Sean B. Palmer, Devarshi Pant, Nigel Peck, Anne Pemberton, David Poehlman, Ian Pouncey, Charles Pritchard, Kerstin Probiesch, W Reagan, Adam Victor Reed, Chris Reeve, Chris Ridpath, Lee Roberts, Mark Rogers, Raph de Rooij, Gregory J. Rosmaita, Matthew Ross, Sharron Rush, Joel Sanda, Janina Sajka, Roberto Scano, Gordon Schantz, Tim van Schie, Wolf Schmidt, Stefan Schnabel, Cynthia Shelly, Glenda Sims, John Slatin, Becky Smith, Jared Smith, Andi Snow-Weaver, Neil Soiffer, Mike Squillace, Michael Stenitzer, Diane Stottlemyer, Christophe Strobbe, Sarah J Swierenga, Jim Thatcher, Terry Thompson, Justin Thorp, David Todd, Mary Utt, Jean Vanderdonckt, Carlos A Velasco, Eric Velleman, Gijs Veyfeyken, Dena Wainwright, Paul Walsch, Daman Wandke, Richard Warren, Elle Waters, Takayuki Watanabe, Gian Wild, David Wooley, Wu Wei, Kenny Zhang, Leona Zumbo.

Enabling funders

This publication has been funded in part with U.S. Federal funds from the Health and Human Services, National Institute on Disability, Independent Living, and Rehabilitation Research (NIDILRR), initially under contract number ED-OSE-10-C-0067 and now under contract number HHSP23301500054C. The content of this publication does not necessarily reflect the views or policies of the U.S. Department of Health and Human Services or the U.S. Department of Education, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government.