Accessibility guide for developers/fr

L’accessibilité est importante pour nos utilisateurs et nous pouvons l’améliorer si nous prenons en compte quelques idées et règles de base. L’accessibilité est difficile dans la mesure où il n’existe pas de normes techniques fixes et universellement acceptées qui fonctionnent réellement de manière cohérente et pour tous les utilisateurs. Cette page ne répertorie ni ne discute des problèmes d’accessibilité spécifiques dans MediaWiki. Elle tente de se concentrer sur les choix technologiques et les choses à faire et à ne pas faire pour éviter les problèmes d’accessibilité.

En termes de développement, je pense que ceci devrait être notre livre de règles :


 * Essayez d’activer nos utilisateurs (et cela signifie tous).
 * Essayez de contourner les problèmes d’accessibilité si cela est possible, mais pas à tout prix.
 * Nous devrions utiliser une approche d’amélioration progressive plutôt que de tolérance aux pannes.
 * Mettre en œuvre des choses qui sont technologiquement solides.



Fonctionnement de l'accessibilité
Quelques concepts importants que vous devez garder à l’esprit.



Des mesures d’accessibilité sous de nombreuses formes
L’accessibilité concerne une variété de choses, veuillez considérer ce qui suit :


 * Quelque chose doit être compréhensible : c’est-à-dire textuellement, visuellement, logiquement et en complexité.
 * Certains utilisateurs ont besoin d'un lecteur d'écran pour interagir, mais d'autres ont tout autant, sinon plus besoin: d'une loupe, d'un contraste plus élevé, d'un moteur de synthèse vocale, de paramètres CSS personnalisés ou d'un type particulier de clavier/d'appareil de saisie.
 * Il doit être accessible ; la réactivité, l’abordabilité, l’emplacement, la langue, le matériel, etc.

En résumé, l’accessibilité n’est pas seulement l’accessibilité du clavier, ou seulement l’accessibilité du lecteur d’écran. Nous nous concentrons souvent sur ces deux, car ils sont facilement négligés traditionnellement. Mais ces problèmes peuvent également être résolus et constituent souvent la base de tout autre type d’améliorations possibles.

Certains problèmes d’accessibilité ont tendance à être des problèmes de conception de produits, de choix stratégiques, de public cible, etc. Comme ces domaines sont plus difficiles à saisir dans des règles écrites qui s’appliquent universellement à l’écosystème MediaWiki, ils sortent du cadre de ce document.



Navigation au clavier
C’est ce que nous appelons la navigation au clavier, mais ce que cela signifie vraiment, c’est : ne vous fiez pas à un dispositif de pointage (tactile, souris).


 * La navigation au clavier consiste à manipuler le focus et à exécuter des actions avec votre clavier.
 * Les éléments qui sont tabulables sont focalisables, mais tout ce qui est focalisable n'est pas tabulable.
 * Tout ce que vous pouvez faire avec une souris devrait être possible avec un clavier.
 * Les informations relatives à la navigation au clavier peuvent être utilisées par les lecteurs d'écran pour améliorer leur expérience.



Lecteur d'écran

 * Un lecteur d'écran utilise un 'curseur' différent, qui parcourt habituellement la structure logique du DOM (Document Object Model).
 * Le focus tend à suivre le curseur du lecteur d'écran et réciproquement mais ce sont deux choses différentes.
 * You can keep track of the focused element by setting a live expression in Chrome
 * Un lecteur d'écran utilise les APIs d' 'accessibilité', que vous pouvez considérer comme étant la vue d'entrée / sortie par dessus le DOM initial.
 * ARIA sont des annotations DOM qui étendent ou orientent la manière dont la logique DOM est modifiée dans les APIs d'accessibilité. Ce n'est pas une alternative à la réécriture d'un nouveau code HTML et JavaScript. La navigation au clavier se fait simplement dans l'ordre logique du DOM ! Pour en savoir plus sur ARIA voir les explications sur w3.org et sur MDN.
 * Un lecteur d'écran n'est pas limité à la navigation dans la structure logique du DOM, mais c'est le fonctionnement par défaut.
 * Un lecteur d'écran peut lire par exemple ce qui se trouve sous le pointeur de la souris.
 * VoiceOver pour iOS utilise un curseur d'écran dirigé par le positionnement du pouce et les mouvements sur l'écran tactile.
 * La plupart des logiciels lecteurs d'écran possèdent des modes de navigation supplémentaires, où vous pouvez lister et naviguer parmi des zones prédéfinies, ou par un sommaire auto-généré, ou encore à l'aide de 'signets' utilisateur définis à l'intérieur d'une page.
 * 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:
 * a long sentence [image] the above image shows...
 * a long sentence [image][image] the left image shows, the right image shows...
 * a long sentence [image][image] the right image shows, the left image shows...
 * a long sentence [image][image] the above image shows...
 * a long sentence [image][image][image] the left image shows, the right image shows...
 * a long sentence [image][image] something totally different. the left image shows, the right image shows...



Règles du développement
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.



Utiliser ou fournir toujours

 * Proper semantic HTML element
 * Use HTML elements for their intended purpose. For example:
 * Use and not  or  or  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  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.
 * There should be no gaps in the nesting of the heading levels (So no H2->H4)
 * Headings should be descriptive
 * Headings should be unique within their own level. (There should not be two H3's with the same content under the same H2 section)
 * There should be separation between navigation and content


 * 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.


 * 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.


 * ,  and   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  state.
 * Don't use  otherwise.
 * If you define any pseudo class, like :hover or :active, please also define a  style.


 * Keyboard navigation
 * Interactive elements of a page should be navigable by keyboard. Please make sure tab key navigation is enabled in your browser and allows you to control each interactive element without making use of a pointing device.
 * Use tabIndex: 0 to make elements keyboard accessible, which are not keyboard accessible implicitly (Anything but, , , , , , and ).
 * In this case also add a keydown handler responding to Enter (keyCode 13) and space (keyCode 32).
 * Use tabindex: -1 to remove elements from accessibility. (use this on links that are labels for the action inside an li for instance)
 * 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
 * The dialog itself should have
 * The dialog should be inserted in DOM order, 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:
 * A guide to understanding and implementing Web Content Accessibility Guidelines 2.0
 * WCAG 2.1 supplement
 * Techniques and Failures for Web Content Accessibility Guidelines 2.0
 * WCAG 2.1 supplement



À ne pas faire

 * There is common advice to use  to push something (often the labels of icon buttons) out of the viewport for visual users and still have it in the accessibility DOM.   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,  is preferred over   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 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  might be an idea in this case ?).
 * with an onclick handler. VO reads such JS as "internal link Hide". Use a proper button, or, 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.

Eviter

 * 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).

Considérez

 * ARIA Roles
 * If a div or span behaves like an actual button use . also   and
 * Be careful with roles. For instance, don't add  to a  element, since the  element has an implicit , which will be overwritten. Instead use nested elements. Similarly for  which has an implicit
 * If a button creates a popupdialog, use.
 * Use  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



Voir aussi

 * Wikimedia Design Style Guide: Accessibility principles
 * Open bugs and feature requests related to the accessibility in MediaWiki and other Wikimedia software
 * W3C Web Accessibility Initiative: Tips for Getting Started
 * W3C Web Accessibility Initiative: Web Accessibility Evaluation Tools List
 * Firefox Developer Tools: Accessibility Inspector
 * Chrome Developer Tools: Accessibility features
 * Accessibility and usability cleanup
 * Blogposts
 * Steps Towards an Accessible Web Form
 * Understanding WCAG Level
 * Software
 * WAVE, a Web accessibility evaluation tool
 * Accessibility simulation on MediaWiki. Experience a page as a color blind person would experience it.
 * https://www.deque.com/axe/ browser extension for accessibility auditing a page
 * https://www.powermapper.com/products/sortsite/checks/accessibility-checks/ webapp for accessibility auditing. See also https://www.powermapper.com/tests/
 * University of Cambridge - Impairment simulator software (Microsoft Windows only)
 * Guides by 3rd parties
 * Designing accessible services by UK Home Office
 * Inclusive Design by Microsoft