accesskey _ mod _ content

General concepts of WCAG 2.0

Any technology that could create accessible content, not only W3C technologies.

Some parts of the WCAG 1.0 not adapted well to the existing situations doing that, in certain respects, have become obsolete. Version 2.0 incorporates all lessons learned from that version 1.0 came to light and takes into account that the web technologies have made progress over the past few years and continue to do so in future.

The WCAG 2.0 have been developed as long-lasting, thus providing a standard web stable over time. In order to achieve this, it has eliminated any aspect relating to specific technologies. The objective is to ensure that the WCAG 2.0 are independent of the technology, using a neutral language without references to specific technologies.

Therefore, the accessibility standards Web content accessibility guidelines (WCAG) 2.0, due to their abstraction, apply both to the W3C technologies and technologies developed outside the W3C. Moreover, there are also applicable to both web technologies present and future.

The WCAG 2.0 are structured as follows:


The WCAG 2.0 are organized into four principles that shape on fundamental concepts underlying accessibility: Visible, Operable, Understandable and robust.

  • Visible: Information and user interface components need to be presented to users so that they can receive.
  • Operable: The user interface components and navigation must be operables.
  • Understandable: information and the handling of the user interface should be understandable.
  • Robust: The content must be sufficiently robust as to enable it to be interpreted faithfully by a wide range of user agents, including products of support.


Within each principle are guidelines of accessibility. These guidelines constitute the basic objectives that must be fulfilled in order to reach a website accessible.

Criteria in accordance

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

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

Each criterion is assigned a level of compliance on how to affect the accessibility of a website if that approach is not met. That is, depending on the impact on affordability.

There are three levels in accordance:

  • The criteria of level are of utmost importance in terms of accessibility to the end, which is basic prerequisites for some users can use the Web.
  • The criteria for level AA must be observed if we want to remove major barriers to accessibility.
  • The criteria of AAA level are the minor but whether they are entrusted to the Site a good level of accessibility.


The WCAG 2.0 tft incorporate the concept " consistent with the accessibility ".

A technology is " consistent with the accessibility "if you have the characteristics necessary to generate content accessible and furthermore browsers, user applications and products of the existing support they are able to understand the technology and provide the information that is accessible to users who request it.

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

Thus, for example, other technology that is also compatible with the accessibility is the PDF format and consists of numerous characteristics in order to generate PDF documents accessible and interpretable by support outputs as screen readers.

In the WCAG 2.0 is not restricted the use of web technologies only to proprietary technologies of the W3C, but allows the use of any technology web consistent with the accessibility on the assumption that:

  • The technology used in an accessible way : how used has been tested and is compatible with the support outputs employees by users.
  • Available browsers, applications and user support outputs that support such technology: that is, the user applications must have native support for the accessibility features of technology, be widely disseminated or be available for download or shop at the same ease and price for persons with disabilities and for a person without a disability. The same is true that required a plugin for access to technology.

Thus, apart from W3C standards for the creation of web pages (HTML, XHTML, CSS, etc.) are no further technologies that create accessible content. For example, you may create accessible documents in PDF format or using JavaScript following a series of good practices to generate content accessible.

Yes, but with certain conditions. You can use technologies that are not as long as they are not dependent on them. That is accessible alternatives to the content included on technologies that are not used or not accessible.

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

No, it is not enough. In Addition, the content is not accessible cannot interfere with the rest of the contents of the page. For example, a Flash animation unreachable can have an alternative text but the animation in itself, even taking alternative, may not contain flashes which can lead to attacks on people with epilepsy fotosensitiva.

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

These criteria in accordance with “ non-interference ” require that:

  • Any content that may cause flashes epileptic seizures
  • No content to generate a trap for the keyboard focus. In other words, no content may stop using the keyboard tab.
  • 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 screen readers, or audio stop in a few seconds or provides a mechanism accessible to stop it or to control their reproduction.