Accessibility guide for developers
||I intend to gather a set of tips and guidelines designed for MediaWiki developers to write code (interfaces) that are more accessible. Perhaps a checklist...|
Accessibility is important for our users and most of it is easy to facilitate if we just take into account a few basic ideas and rules. Accessibility is also very difficult in that there are no fixed and universally excepted technical standards. This page does not list or discuss specific accessibility problems in MediaWiki. It attempts to focus on technology choices and on 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 for every price
- We should use an approach of Progressive enhancement over that of Graceful degradation.
- Implement things that are technological sound
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.
- Logical header structure
- All pages should always have a logical and consistent header structure.
- 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
- null value if purely decorative; or move to CSS background image)
- title attribute for links
- Use the proper HTML element
- use the HTML element fitting the function (so you should prefer <button> elements over span, div and a elements)
- The focus pseudo class
- if you use :hover, also use :pseudo
- Use lang and hreflang attributes
- 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.
- 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
- WCAG 2.0 guidelines
- follow wherever possible
- There is common advise to use -1000px to push something out of the viewport for visual users and still have it in the accessibility DOM. This is BAD advice, it 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.
- Unicode symbols
- Most assistive technologies are not good with symbols. Therefore, try to avoid characters such as ↑, → or more complex characters, because many screenreader 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.
- 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/
See also 
- Open bugs related to the accessibility of MediaWiki
- Firefox accessibility evalutation toolbar-extension. Can be helpful to spot the most obvious problems.
- "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)
- WebAIM Screenreader survey listed Wikipedia as favorite #3 of it's respondents group and did not list it in 'Sites to be avoided'.
- "The German version of the free encyclopedia Wikipedia http://de.wikipedia.org is for many users with disabilities, to an acceptable degree, a useful and operable website." - German Language Wikipedia Accessibility Test According to WCAG 2.0 by Third Age Online.