Guía de accesibilidad para desarrolladores

From mediawiki.org
This page is a translated version of the page Accessibility guide for developers and the translation is 66% complete.

La accesibilidad es importante para nuestros usuarios y podemos mejorarla si tenemos en cuenta algunas ideas y reglas básicas. La accesibilidad es difícil en la medida en que no existen estándares técnicos fijos y universalmente aceptados que realmente funcionen de manera consistente y para todos los usuarios. Esta página no enumera ni discute problemas específicos de accesibilidad en MediaWiki. Intenta centrarse en las opciones tecnológicas y en lo que se debe y no se debe hacer para prevenir problemas de accesibilidad.

En términos de desarrollo, creo que este debería ser nuestro libro de reglas:

  • Intentar habilitar a nuestros usuarios (y eso significa a todos ellos)
  • Intentar evitar los problemas de accesibilidad si es posible, pero no a toda costa
  • We should use an approach of Progressive enhancement over that of Graceful degradation.
  • Implementar cosas que son tecnológicamente apropiadas.

Como funciona la accesibilidad

Algunos conceptos importantes que te tendría que mantener en mente.

Medidas de accesibilidad en muchas formas

La accesibilidad es una variedad de cosas, por favor considere lo siguiente:

  • Algo debería ser comprensible: Eso quiere decir textualmente, visualmente, lógicamente y en complejidad.
  • Algunos usuarios necesitan un lector de pantalla para interactuar, también, sino más comunes son: una lupa, alto contraste, software texto a voz (text-to-speech), ajustes CSS personalizados o un teclado/dispositivo de entrada especial.
  • It needs to be reachable; responsiveness, affordability, location, language, hardware, etc.

En resumen, la accesibilidad no es sólo accesibilidad de teclado o sólo accesibilidad de lector de pantalla. A menudo nos enfocamos en esos dos porque, tradicionalmente, son más fáciles de pasar por alto. Pero estos asuntos también son solucionables y a menudo proporcionan las bases para cualquier otra clase de mejoras posibles.

Algunos problemas de accesibilidad tienden a ser problemas con el diseño del producto, elecciones estratégicas, audiencia objetivo, etc. Como éstas áreas son mas difífiles de capturar en reglas escritas que puedan ser aplicadas universalmente a todo el ecosistema de MediaWiki, las mismas se encuentras fuera del alcance de éste documento.

Navegación de teclado

Llamamos a esto navegación de teclado, pero lo que realmente quiere decir es: No dependa de un dispositivo apuntador (touch, mouse).

  • La navegación de teclado es manipular el enfoque del sitio y ejecutar acciones utilizando su teclado.
  • Elementos en los que se puede utilizar el Tabulador, pueden recibil el foco del cursor, pero no en todos los elementos que pueden recibir el foco del cursor, se puede utilizar el tabulador.
  • Todo lo que sea capaz de hacerse con un mouse debería ser posible con un teclado.
  • La información de la navegación de teclado puede ser usada por los lectores de pantalla para mejorar su experiencia.

Lector de pantalla

  • A screen reader uses a different 'cursor', which usually walks the logical structure of the DOM.
  • El foco tiende a seguir el cursor de lector de la pantalla y viceversa, pero no son iguales.
  • Un lector de pantalla utiliza el 'accesibilidad' APIs, el cual te podría considerar para ser una producción/de entrada 'vista' arriba del normal DOM.
  • ARIA are DOM annotations that enhance or manipulate how the DOM logic is transformed into the accessibility APIs. No es una alternativa escribir apropiadamente en HTML y Javascript. ¡La navegación de teclado es sencillamente conseguida por orden lógico el DOMǃ For more on ARIA see w3.org explanation and MDN explanation.
  • Un lector de pantalla no está limitado a navegar por la estructura lógica DOM, solo es por efecto.
    • Un lector de pantalla puede leer lo que está bajo el puntero del ratón por caso.
    • VoiceOver para iOS usa un cursor de pantalla que es manipulado por posicionamiento de pulgar y gestos en la pantalla táctil.
    • La mayoría de software de lectura de pantalla tiene modos de navegación adicionales, donde puedes listar y navegar por áreas de referencia, una tabla de contenidos auto-generada, o incluso marcadores definidos por el usuario dentro de una página.
  • From the above point of multiple navigation methods, follows: There is a beginning and an end, but also left, right, top and bottom. You should not rely on these in your communication too much, but you don't need to fully deny their existence either. Do not confuse the visual capabilities of the user with spatial awareness that the screen reader might be able to convey to the user. Example:
    1. a long sentence [image] the above image shows... Still acceptable
    2. a long sentence [image][image] the left image shows, the right image shows... Still acceptable
    3. a long sentence [image][image] the right image shows, the left image shows... Not acceptable
    4. a long sentence [image][image] the above image shows... Not acceptable
    5. a long sentence [image][image][image] the left image shows, the right image shows... Not acceptable
    6. a long sentence [image][image] something totally different. the left image shows, the right image shows... Definitely not acceptable

Versiones de desarrollo

There are several standards around accessibility and honestly, almost all of them, although sound on identifying issues, still have significant problems when it comes to technical solutions (They have a high ratio of 'ugly workarounds'). This has been cause of much controversy in the communities. As such, we should identify uncontroversial stuff that we should simply always (or never) do and why. It's much easier to reach certain goals if we separate the uncontroversial stuff from the controversial stuff.

Hacer uso o proporcionar siempre

Proper semantic HTML element
Use HTML elements for their intended purpose. For example:
  • Use ‎<button> and not ‎<div> or ‎<span> or ‎<a> with a click handler
  • If you feel the need to bold something, consider if it is not more appropriate to use a header or a strong element
Logical heading structure
All pages should always have a logical and consistent heading structure. Headings are one of the primary navigation tools used by screen reader users.
  1. There should be no gaps in the nesting of the heading levels (So no H2->H4)
  2. Headings should be descriptive
  3. Headings should be unique within their own level. (There should not be two H3's with the same content under the same H2 section)
  4. There should be separation between navigation and content
alt attribute for images with meaningful values
If an image is decorative, use an explicit empty value for the alt attribute; even better, turn it into a CSS background image.
the image alt usually takes precedence over the title attribute of images and even over the title attribute of links that wrap an image.
title attribute for links
These are usually shown as the tooltips
Only use titles if they differ from the link text.
Most link titles are not actually spoken by screen readers, unless the reader has been explicitly configured this way.
lang, dir and hreflang attributes
Using lang and hreflang enables selecting a proper voice in screen readers, picks the right spelling correction in browsers etc.
Sufficient contrast
Always check your colors for sufficient contrast. For text, a higher contrast is needed for smaller text (due to anti-aliasing).
Focus for keyboard navigation
Do not remove outline from focusable elements unless you define your own outline for the :focus state.
  • Don't use outline: 0 otherwise.
  • If you define any pseudo class, like :hover or :active, please also define a :focus style.
Keyboard navigation
The tools should be navigable by keyboard. Please turn that on in your browser if you are a developer.
  1. Use tabIndex: 0 to make elements keyboard accessible, which are not keyboard accessible implicitly (Anything but ‎<a>, ‎<area>, ‎<button>, ‎<input>, ‎<object>, ‎<select>, and ‎<textarea>).
    1. In this case also add a keydown handler responding to Enter (keyCode 13) and space (keyCode 32).
  2. Use tabindex: -1 to remove elements from accessibility. (use this on links that are labels for the action inside an li for instance)
  3. Elements that are implicitly keyboard accessible will forward enter/space keydown to the click handler
Dialogs etc

When not taking good care of accessibility, dialogs are some of the most inaccessible elements for screen reader and keyboard users. Spend some time on this.

  • The element that opens the dialog should have aria-haspopup
  • The dialog itself should have role=[dialog | alertdialog | tooltip]
  • The dialog should be inserted in DOM order,[1] or aria owns/controls needs to specify this relation between opening element and dialog
  • When opening the dialog, remember last focused element and shift focus to the first focusable tabbable element inside the dialog
  • When the dialog is modal, make it impossible to interact with the rest of the page
    • Capture clicks outside the dialog and ignore them or let them dismiss the dialog
    • Make sure you cannot tab to links or input elements outside of dialog
    • Make elements outside of the dialog unreachable for screen reader, by using aria-hidden
  • Make sure there is a close mode (esc key and a focusable close button with a descriptive title)
  • Closing should return the (keyboard) focus to the original focus point that you stored when you opened the dialog. For screen readers to return to the same point, be sure to specify the right owner of the dialog, if you have not inserted the dialog in DOM order.
  • Read up: Aria modals, Aria modal dialog, ARIA nonmodal dialog, ARIA tooltips.
WCAG 2.1 guidelines
Follow wherever possible
And its accompanying documents:

No

  • There is common advice to use left: -1000px to push something (often the labels of icon buttons) out of the viewport for visual users and still have it in the accessibility DOM. text-indent: -9999px is variant of this. This is BAD advice.
    • This breaks our RTL rendering in several browsers. Specifically in rtl mode it creates a large canvas left of the viewport and scrollbars, much as +1000px would create in ltr mode. (If needed, top: -1000px is preferred over left: -1000px to avoid this).
    • VoiceOver on mobile is unable to use this text as a fallback, since it is a 'positional' screen reader. You cannot move your finger over this text and thus the text will not be read either. (aria-label is often the better choice).
    • Lastly, this enlarges the render surface needed to calculate the final webpage and this can impact performance [1] on mobile devices.
    • Insightful overview of 'hide text offscreen' tricks are given by Jonathan Snook.
  • Things should not be repeated often. If you have a 100 links on a page that can open a dialog, then don't add 100 labels to those 100 links telling the user that it can be used to open a dialog. Telling a user how to use/what to do with the interface is a good thing, doing it consistently is simply annoying. Find a different way to explain it once (an aria-live=polite might be an idea in this case ?).
  • <a href="#">Hide</a> with an onclick handler. VO reads such JS as "internal link Hide". Use a proper button, or <a role="button" tabindex="0">Hide</a>, with 'space' and 'enter' key handlers in the onclick. But no href attribute.
  • Do not nest interactive functionality inside another interactive element (links or buttons inside links). This confuses screen readers.

Evite

Unicode symbols
Most assistive technologies are not good with symbols. Therefore, try to avoid characters such as ↑, →‎ or more complex characters, because many screen reader won't understand them. If they are required, try to wrap with a span element with the title attribute, so that the title attribute can communicate the implicit meaning within the context to the reader.
Small fonts
Legibility is preferred. If you make something so small that it is hard to read, do you even need it to begin with? Also avoid small fonts with low or mediocre contrast values (even if they fall inside the WCAG guidelines, small sizes require more explicit contrast then large sizes, especially with anti aliasing enabled).
Unusually large fonts
If you make text much larger than normal, it can become similarly hard to read (unless it's very short). This applies mostly to body text, or anything that takes up more than a couple lines. But the larger the text is, the more lines it will take up.
tabIndex > 0
DOM order is preferred wherever possible. DOM order provides context for the actions.
Workarounds
Traditionally, accomplishing 'full' accessibility has required a lot of workarounds for html itself, the browsers and even specific screenreader software. However these workarounds often come with side effects, make use of bugs or unspecified behavior and inevitably create technical debt.
MediaWiki, because of the users it seeks to serve, the amount of code, it's (lack) of funding, etc tends to prefer future proof code over code that easily breaks. As such it generally avoids workarounds even if that might sometimes limit the accessibility we can deliver. Decisions on this are often influenced by the relative audience of the feature in MediaWiki. If something is ubiquitous for all users a workaround is more warrented than if the feature affected is only used by a tiny part of the audience (for instance, reading a page vs modifying the configuration of the installation).

Considera

  • ARIA Roles
    • If a div or span behaves like an actual button use role="button". also role="dialog" and role="alert"
    • Be careful with roles. For instance, don't add role="button" to a ‎<th> element, since the ‎<th> element has an implicit role="columnheader", which will be overwritten. Instead use nested elements. Similarly for ‎<li> which has an implicit role="listitem"
    • If a button creates a popupdialog, use aria-haspopup.
    • Use aria-labelled-by for contexts where this is not fully logical by itself (so everywhere except for labels in forms and headers in tables).
  • Avoid tables for layout purposes and test on smaller screen widths.
  • hide stuff: https://www.tpgi.com/html5-accessibility-chops-hidden-and-aria-hidden/
  • skip/jump to links

Véase también

Referencias

  1. DOM order defined and discussed here and here