Accessibility guide for developers

Accessibility is important for our users and we can facilitate it if we take into account a few basic ideas and rules. Accessibility is difficult insofar as are no fixed and universally accepted technical standards that actually work consistently and for all users. This page does not list or discuss specific accessibility problems in MediaWiki. It attempts to focus on technology choices and Do's and Don'ts to prevent accessibility problems.

In terms of development, I think this should be our rule book:
 * Try to enable our users (and that means all of them)
 * Try to work around issues of accessibility if that is possible, but not at all costs
 * We should use an approach of Progressive enhancement over that of Graceful degradation.
 * Implement things that are technological sound

We should never forget that we already are considered to be quite accessible.

How accessibility works
Some important concepts that you should keep in mind.

Accessibility measurements in many forms
Accessibility is about a variety of things, please consider the following: In summary, accessibility is not only keyboard accessibility or only screen reader accessibility
 * Something should be understandable: that means textually, visually, logically and in complexity.
 * Some users need a screen reader to interact, but just as, if not more common are: a loupe, higher contrast, a text to speech engine, custom CSS settings, or a special type of keyboard/input device.

Keyboard navigation
We call this keyboard navigation, but what it really means is: Don't rely on a pointer device (touch, mouse).
 * Keyboard navigation is about manipulating the focus and executing actions with your keyboard.
 * Elements that are tabable are focusable, but not everything that is focusable is tabable.
 * Everything you are able to do with a mouse should be possible to do with a keyboard.
 * Keyboard navigation information can be used by screen readers to enhance their experience.

Screen reader

 * A screen reader uses a different 'cursor', which usually walks the logical structure of the DOM.
 * The focus tends to follow the screen reader cursor and vice versa, but they are not the same
 * A screen reader uses the 'accessibility' APIs, which you could consider to be a input/output 'view' on top of the normal DOM.
 * ARIA are DOM annotations that enhance or manipulate how the DOM logic is transformed into the accessibility APIs. It is not an alternative to writing proper HTML and Javascript. For more on ARIA see here and here.
 * ARIA is still young. Do not rely on it too much. Keyboard navigation and a logical DOM are good fallbacks to have for screen readers.
 * 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, and VoiceOver for iOS uses a screen curser that is manipulated by thumb positioning and gestures on the touch screen. It can navigate by landmark areas, an auto generated ToC, or even user defined 'bookmarks' inside a page.
 * From the above point of multiple navigation methods, follows: There is beginning and 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][image] the left image shows, the right image shows...
 * a long sentence [image][image][image] the left image shows, the right image shows...

Development guidelines
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.

Always

 * Use the proper HTML element : Use the HTML element fitting the function (so you should prefer  elements over ,   and   elements)
 * 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
 * Use a tool like Firefox accessibility evaluation toolbar to easily inspect the structure of all headers.


 * alt attribute for images : 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. some tests


 * 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


 * Contrast : Always check your colors for sufficient contrast. For text, a higher contrast is needed for smaller text (due to anti-aliasing).
 * The focus pseudo class : If you define :hover styling, you usually should also define a :focus style
 * Focus outline : Do not remove outline from focusable elements unless you define your own outline for the :focus state
 * Use lang and hreflang attributes : Using lang and hreflang enables selecting a proper voice in screen readers, picks the right spelling correction in browsers etc.
 * Use lists for logically grouped data : move hlist of en.wp into core to facilitate this?
 * 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 form 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

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.
 * Bolding and notes : If you feel the need to bold something, consider if it is not more appropriate to use a header or a strong/em element
 * Dialogs etc
 * 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, 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 it's 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

Don't

 * There is common advise 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 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 tell it once (an aria-live=polite 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.

Avoid

 * Unicode symbols : Most assistive technologies are not good with symbols. Therefore, try to avoid characters such as &uarr;, →‎ 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.

Consider

 * 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  element, since the   element has an implicit role="columnheader", which will be overwritten. Instead use role="columnheader button". Similarly for  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 but for labels in forms and headers in tables).
 * Avoid tables for layout purposes. We have some places where they are hard to get rid of (use WAI-ARAI ?)
 * hide stuff: http://www.paciellogroup.com/blog/2012/05/html5-accessibility-chops-hidden-and-aria-hidden/
 * skip/jump to links

Things to discuss

 * Roving tabindex vs. aria-activedescendant (roving more compatible, aria-activedescendant more 'compatible?'
 * Usage of . in labels. Ending a label with a dot, causes the screen reader to make a fullstop. See also: 24592 where the lack of fullstops creates unintelligible sentences.
 * It seems that setting the ariaProperties with .prop isn't working in at least Safari+VoiceOver. Possible root cause, the DOM is duplicated and .prop only updates the plain DOM object, not the accessibility DOM object ?
 * aria-label is not used by JAWS (14) if you put it on a span (with contents?). The element needs to be either a control/widget or to have a role. TheDJ (talk) 13:44, 18 August 2013 (UTC)

Known bugs

 * aria-pressed + role button is not supported in webkit/Safari 115292 (Fixed upstream april 2015)

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)