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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.

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:


Las WCAG 2.0 están organizadas en cuatro principios que conforman los conceptos fundamentales sobre los que se asienta la accesibilidad: Perceptible, Operable, Comprensible y Robusto.

  • 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: Los componentes de la interfaz de usuario y la navegación deben ser operables.
  • Comprensible: La información y el manejo de la interfaz de usuario debe ser comprensible.
  • 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.
  • The criteria for level AA must be observed if we want to remove major barriers to access.
  • Los criterios de nivel AAA son los de menor importancia, pero si se cumplen confieren a la Web un buen nivel de accesibilidad.


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.

Así, por ejemplo, otra tecnología que también es compatible con la accesibilidad es el formato PDF ya que dispone de numerosas características para poder generar documentos PDF accesibles e interpretables por productos de apoyo como los lectores de pantalla.

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.

Sí, pero con ciertas condiciones. Se pueden utilizar tecnologías no accesibles siempre y cuando no se dependa de ellas. Es decir, que existan alternativas accesibles para el contenido que se incluya con tecnologías no accesibles o utilizadas de forma no accesible.

Por ejemplo, se puede incluir un documento PDF que no haya sido creado de forma accesible o en un formato diferente que no sea compatible con la accesibilidad. Sin embargo, en este caso es necesario proporcionar la misma información en un formato accesible, por ejemplo mediante HTML y CSS.

No, no es suficiente. Adicionalmente, el contenido no accesible no puede interferir con el resto de contenidos de la página. Por ejemplo, una animación Flash no accesible puede disponer de una alternativa textual pero la animación en sí misma, aún teniendo alternativa, no puede contener destellos ya que podría provocar ataques a las personas con epilepsia fotosensitiva.

Así, existen una serie de criterios de conformidad que son aplicables a todo el contenido de la página, aunque se trate de contenido no accesible pero con una alternativa accesible, porque un fallo en cualquiera de estos criterios podría interferir con el uso de toda página.

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