Accessibility guide for developers/de

Barrierefreiheit ist wichtig für unsere Nutzer und wir können sie verbessern, wenn wir einige grundlegende Ideen und Regeln berücksichtigen. Barrierefreiheit ist insofern schwierig, als es keine festen und allgemein akzeptierten technischen Standards gibt, die tatsächlich einheitlich und für alle Nutzer funktionieren. Auf dieser Seite werden keine spezifischen Probleme mit der Barrierefreiheit in MediaWiki listet oder diskutiert. Es wird versucht, sich auf die Auswahl von Technologien und die "Dos and Don'ts" zur Vermeidung von Barrieremöglichkeiten zu konzentrieren.

Was die Entwicklung betrifft, so sollte dies unser Regelwerk sein:


 * Versuchen Sie, unseren Nutzern (und damit sind alle gemeint) den Zugang zu erleichtern
 * Versuchen Sie, Probleme der Unzugänglichkeit zu umgehen, wenn dies möglich ist, aber nicht um jeden Preis.
 * Wir sollten die Herangehensweise der progressiven Verbesserung gegenüber der, der würdevollen Verschlechterung
 * Implementieren Sie Dinge die technisch sinnvoll/vernünftig sind

Wie Barrierefreiheit funktioniert
Einige wichtige Konzepte, die Sie im Hinterkopf behalten sollten.

Zugänglichkeitsmessungen in vielen Formen
Barrierefreiheit hat mit vielen Dingen zu tun, bitte stellen Sie sich folgendes vor:


 * Einiges sollte verständlich sein: das heißt Textbezug, visuelle Darstellung, Logik und Komplexität.
 * Einige Benutzer benötigen ein Bildschirmlesegerät, um zu interagieren, aber genauso häufig, wenn nicht sogar häufiger, sind: eine Lupe, ein höherer Kontrast, eine Text-to-Speech-Engine (Text zu Sprache), benutzerdefinierte CSS-Einstellungen oder eine spezielle Art von Tastatur/Eingabegerät.
 * Sie muss erreichbar sein: anpassbar, erschwinglich, Standort und Spracheabhänging, Hardware angepasst usw.

Zusammenfassend lässt sich sagen, dass Zugänglichkeit nicht "nur" Tastaturzugänglichkeit "oder nur" Bildschirmlesezugänglichkeit bedeutet. Wir konzentrieren uns oft auf diese beiden, weil sie traditionell leicht übersehen werden. Aber auch diese Probleme sind lösbar und bilden oft die Grundlage um andere Verbesserungen möglich zu machen.

Einige Probleme mit der Zugänglichkeit sind eher Probleme mit dem Produktdesign, strategischen Entscheidungen, der Zielgruppe usw. Da diese Bereiche schwieriger in niedergeschriebenen Regeln zu erfassen sind, die universell für das MediaWiki Ökosystem gelten, liegen sie außerhalb des Rahmens dieses Dokuments.

Tastaturnavigation
Wir nennen das Tastaturnavigation, aber was es wirklich bedeutet, ist: Verlassen Sie sich nicht auf ein Zeigergerät (Touch, Maus).


 * Bei der Tastaturnavigation geht es darum, den Fokus zu manipulieren und Aktionen mit der Tastatur auszuführen.
 * Elemente, die man "antippen/klicken kann" können auch fokussiert werden, aber nicht alles, was fokussiert werden kann, kann auch angetippt werden.
 * Alles, was man mit einer Maus machen kann, sollte auch mit einer Tastatur möglich sein.
 * Die Informationen zur Tastaturnavigation können von Bildschirmlesegeräten genutzt werden, um die Benutzerfreundlichkeit zu erhöhen.

Bildschirm Leser

 * Eine Vorleseanwendung verwendet einen anderen "Cursor", welcher meist der logischen Struktur des DOM folgt.
 * Der Fokus neigt dazu dem Cursor der Vorleseanwendung zu folgen (und umgekehrt), aber sie sind nicht die selben.
 * Eine Vorleseanwendung nutzt die Barrierefreiheit APIs, welche man als Eingabe/Ausgabe "Ansicht" sehen kann, welche dem normalen DOM übergeordnet ist.
 * ARIA sind DOM-Annotationen welche die Umwandlung der DOM-Logik in die APIs für Barrierefreiheit verbessert oder beeinflusst. Es ist keine Alternative dazu, richtiges HTML und JavaScript zu entwickeln. Tastaturnavigation wird durch die logische DOM-Reihenfolge erreicht. Für mehr zu ARIA siehe auch w3.org Erklärung und MDN Erklärung
 * A screen reader is not limited to navigating by the logical DOM structure, it's just the default.
 * A screen reader can read what is under the mouse pointer for instance
 * VoiceOver for iOS uses a screen cursor that is manipulated by thumb positioning and gestures on the touch screen.
 * Most screen reader software has additional navigation modes, where you can list and navigate by landmark areas, an auto-generated Table of Contents, or even user defined 'bookmarks' inside a 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...

Entwicklungs Richtlinien
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.

Verwenden oder bereitstelle immer

 * 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 :The tools should be navigable by keyboard. Please turn that on in your browser if you are a developer.
 * 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

Nicht

 * 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.

Vermeide

 * 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).

Bedenke

 * 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

Siehe auch
 * 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)

Papers

 * "Making Wikipedia editing easier for the blind". 2008. M. Claudia Buzzi, Marina Buzzi. IIT-National Research Council. DOI:10.1145/1463160.1463210
 * "Is Wikipedia Usable for the Blind". 2008. Marina Buzzi (IIT), Barbara Leporini (ISTI). p. 15-22.
 * "Wikipedia, the open encyclopaedia: is it really open to blind users?" (Conference paper). 2008. j. ACM. Barbara Leporini. DOI:10.1145/1368044.1368049 (Derived from parent work)

Nachweise