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The general concepts of WCAG 2.0

A cualquier tecnología con la que se pueda crear contenido accesible y no únicamente a tecnologías W3C.

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.

The WCAG 2.0 has been developed with the intention of being lasting, thus providing a standard web stable over time. To achieve this, has been removed any aspect related to specific technologies. The goal is that the WCAG 2.0 are independent of technology, using a neutral language without references to specific technologies.

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.

  • Perceptible: La información y los componentes de la interfaz de usuario tienen que ser presentados a los usuarios de forma que los puedan percibir.
  • Operable: Components of the user interface and navigation must be operable.
  • Comprensible: La información y el manejo de la interfaz de usuario debe ser comprensible.
  • Robusto: El contenido debe ser lo suficientemente robusto como para que pueda ser interpretado de forma fidedigna por una amplia variedad de agentes de usuario, incluyendo los productos de apoyo.


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


Cada pauta contiene a su vez una serie de criterios de conformidad, o requisitos concretos para cumplir las pautas. Estos criterios de conformidad son testeables y se incluyen para permitir que las WCAG 2.0 se puedan usar como referencia cuando sea necesario establecer requisitos de accesibilidad para guías o políticas de diseño, normativas y/o requisitos legales. Es importante señalar que las pautas no son testeables y sólo proporcionan los objetivos generales que permiten a los desarrolladores comprender los criterios de conformidad.

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:

  • Los criterios de nivel A son los de mayor importancia en cuanto a la accesibilidad final, siendo requisitos básicos para que algunos usuarios puedan usar la Web.
  • The criteria for level AA must be observed if we want to remove major barriers to access.
  • 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 " si dispone de las características necesarias para generar contenido accesible y además los navegadores, aplicaciones de usuario y productos de apoyo existentes son capaces de comprender dicha tecnología y proporcionar la información de forma accesible a los usuarios que la requieran.

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 : es decir, la forma en la que se usa ha sido probada y es compatible con los productos de apoyo empleados por los usuarios.
  • 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