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The general concepts of WCAG 2.0

To any technology with which you can create accessible content and not only W3C technologies.

Some parts of the WCAG 1.0 is not entirely well adapted to the current situations doing that, in some respects, have become obsolete. Version 2.0 incorporates all the experience gained since version 1.0 came to light and takes into account that web technologies have made progress over the Last few years and will continue to do so in the future.

Las WCAG 2.0 se han desarrollado con la intención de ser perdurables, proporcionando así un estándar web estable en el tiempo. Para lograrlo, se ha eliminado cualquier aspecto relativo a tecnologías específicas. El objetivo es que las WCAG 2.0 sean independientes de la tecnología, usando un lenguaje neutro sin referencias a tecnologías específicas.

Therefore, the accessibility guidelines for Web content (WCAG) 2.0, due to its abstraction, apply to both the W3C technologies and technologies developed outside the W3C. Also, are also applicable to both web technologies current and future.

The WCAG 2.0 are structured in the following way:


The WCAG 2.0 are organized into four principles that make up the fundamental concepts underlying accessibility: Perceptible, Operable, understandable and Robust.

  • Visible: the information and components of the user interface must be submitted to users so that people can perceive.
  • Operable: Components of the user interface and navigation must be operable.
  • Understandable: information and handling of the user interface must be understandable.
  • Robust: the content must be sufficiently robust as so that it can be reliably interpreted by a wide variety of user agents, including the products of support.


Within each principle are patterns of accessibility. These patterns are the basic objectives that we must comply to achieve a website accessible.


Each pattern contains a series of criteria of conformity, or to meet specific requirements patterns. These criteria in accordance are testeables and are included to allow the WCAG 2.0 can be used as a reference when necessary to establish accessibility requirements for guides or design policies, regulations and/or legal requirements. It is important to note that patterns are not testeables and only provide the overall objectives enabling developers to understand the criteria of conformity.

Unlike the WCAG 1.0, in version 2.0 are not defined priorities but speaks directly from levels of conformity.

Each criterion is assigned a level of line that indicates how it affects the accessibility of a website if the criterion is not met. That is, depending on their impact on accessibility.

There are three levels of line:

  • Standard criteria are the most important regarding final accessibility, basic requirements for some users can use the Web.
  • Los criterios de nivel AA deben ser observados si queremos eliminar importantes barreras de acceso.
  • Standard criteria AAA are the minor but if you meet confer on the Web a good level of accessibility.


The WCAG 2.0 incorporated as a novelty the concept " compatible with accessibility ".

A technology is " compatible with accessibility "if you have the necessary characteristics to generate content accessible and additionally browsers, user applications and existing support products are capable of understanding that technology and provide the information in an accessible to users that need it.

This can be better understood with a simple example. For example, HTML allows you to provide alternative texts to the images through the alt attribute and screen readers are able to access the text and read it aloud to the blind. The same applies to the rest of accessibility features of HTML.

Thus, for example, other technology that is also compatible with accessibility is the PDF format because it has many features for generating PDF documents accessible and interpretable support for products such as screen readers.

In the WCAG 2.0 is not restricted using web technologies only to the technologies of W3C, but allows you to use any web technology that is compatible with accessibility whenever:

  • The technology is used in an accessible : that is, the way in which is used has been tested and is compatible with the support products used by users.
  • Available browsers, username and applications support products that support this technology: i.e. user applications must have native support for accessibility features of technology, be widely disseminated or be available for download or purchase with the same ease and price for persons with disabilities as for a person without disabilities. The same applies in the case that required a plugin for access to technology.

So, apart from the standard W3C for the creation of web pages (HTML, XHTML, CSS, etc.) are more technologies with which you can create content accessible. For example, you can create accessible documents in PDF or using JavaScript following a series of good practices to generate content accessible.

Yes, but under certain conditions. You can use technologies do not accessible if and when does not depend on them. That is to say that alternatives exist accessible to the content that is included with technologies do not accessible or used not accessible.

For example, you can include a PDF document that has not been created in an accessible or in a different format that is not compatible with accessibility. However, in this case it is necessary to provide the same information in an accessible format, for example through HTML and CSS.

No, it is not enough. Additionally, the content not accessible cannot interfere with the rest of the contents of the page. For example, a Flash animation not accessible can have an alternative but the animation in itself, even taking alternative, may not contain glimmers since it could provoke attacks to people with epilepsy fotosensitiva.

Thus, there are a number of criteria that are applicable to all of the content of the page, even if it is not accessible content but with an accessible alternative, because a bug in any of these criteria could interfere with the use of any page.

These criteria of conformity of “ non-interference "require that:

  • Any content that may cause flashes epileptic seizures
  • No content generates a trap for the keyboard focus. That is, any content may interrupt the tab through keyboard.
  • Ningún contenido contendrá movimientos o parpadeos que puedan desorientar a los usuarios o al menos se proporciona un mecanismo para detenerlos o desactivarlos.
  • No content reproduce an audio that might interfere with the screen readers, or the audio will stop in a few seconds or provides a mechanism accessible to stop or control their reproduction.
General access point
General access point