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This document explains how to design accessible XML languages. Compared to the HTML or MathML language, XML is one level up: it is a meta syntax used to describe these languages as well as new ones, and it provides no intrinsic guarantee of device independence or textual alternate support. In this context, guidelines are needed that explain to XML formats and tools designers how to include basic accessibility features - such as the ones present in HTML - in all their new development.
This document is a WAI PF draft note made available by the Protocols and Formats Working Group (PFWG).
Publication of this paper does not imply endorsement by the W3C
membership. A list of current W3C technical reports and publications,
including working drafts and notes, can be found at
http://www.w3.org/TR.
XML (Extensible Markup Language) is a meta-syntax, used to create new languages.
It can be seen as a simplication of SGML (Standard Generalized Markup Language), designed to promote a wider acceptance in Web markets, but serving the same functionality of extensibility and new language design.
HTML (Hyperter Markup Language) is one particular application of SGML, which covers one set of needs ("simple" hypertext documents) and one set of element and attributes.
For instance, in HTML, authors can write elements like:
<TITLE>XML and Accessibility</TITLE> <ADDRESS lang=fr>Daniel Dardailler</ADDRESS> <H1>Background</H1>and they can only use elements (TITLE, H1, etc) defined by the HTML specification (which defines about a hundred), and their attributes.
In SGML and XML, authors can define their own set of elements, and end up with documents like:
<MENU>New England Restaurant</MENU>
<APPETIZER>Clam Showder
<PHOTO url="clam.jpg">A large creamy bowl of clam showder, with
bread crumbs on top</PHOTO>
</APPETIZER>
which may fit more closely the needs of their information system.
Within W3C, the HTML language is now migrating from SGML to XML - this is called XHTML - including a modularization of HTML to suit the needs of a larger community (mobile users, Web TV, etc).
XML is therefore not to be seen as a replacement of HTML, but as a new building layer on top of which HTML is to be placed, next to other languages designed by W3C, such as MathML (for representing mathematical formula), SMIL (for synchronizing multi media), SVG (for scalable graphics), etc., and other new languages designed by other organizations (such a OpenEBook, XML-EDI, etc).
Furthermore, it is important to understand that XML is not only a User Interface technology (like HTML), but can and is often used in protocol communication, to serialize and encode data to be sent from one machine to the other.
The XML grammars (called DTDs - but see the caveat about our use of the term DTD in the definition section) can be classified along two different axes:
According to this taxonomy, these guidelines only address User-centric DTDs. This does not imply that the first type of DTD doesn't have accessibility issues or features (see how XSL can help Braille formatting for instance). However since they are not directly conveying information presented to the end-user, they are out of our scope here.
In a sense, machine-centric DTDs have no connection to user interface accessibility, and one might ask if the commutative proposition is true: DTDs with no accessibility issues are the ones that have reached the right level of machine-centricity.
The WAI (Web Accessibility Initiative) has done extensive work in the HTML area, resulting in lots of new functionalities beind added to the version 4.0 of the language (see the HTML4 Accessibility Improvements paper).
These features includes:
One area of concern with the advent of XML is that the freedom of design it brings will result is a loss of accessibility features, present today because of HTML's pervasive presence and widely available specification.
For instance, one could design a new XML language that would prevent the creation of accessible documents, by not including in the element or attribute set a way to attach an alternate textual description for a photo:
<MENU>New England Restaurant</MENU> <APPETIZER>Clam Showder <PHOTO url="clam.jpg"/> <-- no alt attribute or textual content model here </APPETIZER>In this example, the problem is not that the author of this document didn't put an alt attribute, it's that the designer of the language didn't put the attribute in the language itself.
But let's start by defining what we mean by accessible DTD and documents (Details on these definitions are provided at the end of this document).
An XML DTD is accessible if it enables and promotes the creation of accessible documents
A document is accessible if it can be equally understood by its targeted audience regardless of the device used to access it.
An accessible document is also defined by conforming to the Web Content Accessibility Guidelines.
As explained in the introduction, we're only considering User-centric languages here, and for them, the message is simple: be device independent and export your semantics as much as you can.
While the priority is stronger on the first aspect (multi-modality), both aspects are important, as without the knowledge of the meaning of the XML elements and attributes, there is little chance that alternative user agents can do something intelligent with just the document bits.
This semantics knowledge can be provided through human readable documentation of course, but having machine readable assertions of some semantics that can then be used to present the document in various media is paramount for pervasive access (i.e., you don't need a programmer, you just need a program).
The ICADD (International Committee on Accessible Document Design ) committee was a pioneer in this topic, for SGML accessibility and ways to convey arbitrary DTD semantics (using specific SGML binding mechanisms). A few years later, ICADD has not really been adopted, and people are still trying to solve the same problem, albeit with more experience in the field of HTML accessibility, and applied to XML this time.
This section provides a list of abstract guidelines. Some examples of checkpoints are provided, and detailed checkpoints and techniques that DTD designers can follow to achieve accessibility when designing new XML DTDs still have to be defined by WAI and W3C.
An additional advice we give to DTD designers is that in their specification itself (the documentation) they always emphasize the accessibility features of their new language and try to include accessibility as part of any conformance statement that they introduce (be it for the document themselves, or for readers/editors of the language). See the SVG specification for an example of both practices.
In the presentation of guidelines for XML accessibility, we separate abstract guidelines from implementation techniques. This allows us to talk about the guidelines without spending the time up-front to solve the implementation issues.
The fact is: there are several techniques for achieving the same result and people's decision will be a function of time and product available and their own commitment to access.
For instance, we might want to have the XML designer indicate what constitutes a "list" element in a given markup, and this in turn can be implemented using various techniques:
Along with the choice of the metadata mechanism and vocabulary comes the issue of semantics availability: how does one access the DTD and possible XSLT or schemata from an instance document? This is sometimes referred to as XML packaging or related-resource discovery and is a very important feature for accessibility.
DTD: Even though we use the acronym DTD, we don't want people to assume we are only talking about a DTD as defined in XML 1.0 but rather some document or collection of documents which contains all the references for interpreting a document which is encoded in accordance with the usage of some application or community of discourse. Schema or profile might be a better word for our usage.
An XML DTD is accessible if it enables and promotes the creation of accessible documents
A document is accessible if it can be equally understood by its targeted audience regardless of the device used to access it.
An accessible document is also defined by conforming to the Web Content Accessibility Guidelines.
To take an example, suppose HTML didn't have an ALT attribute on IMG, it would still in theory "enable" the creation of accessible documents, since HTML files carry textual content and one could always describe images inline, as in
<IMG SRC="Tax.gif"> How to pay your taxes
but this doesn't "promote" accessibility as most author will not want to repeat "How to pay your taxes" if the logo already says "How to pay your taxes" (assuming CSS cannot be used for that). Having ALT "promotes" accessibility as it allows images to be described without performance loss - such as duplication - for image viewer.
In any case, accessibility is not just about alternative content, as the next section will show.
This term also potentially carries with it the issues related to high bandwidth availibility (or lack thereof), where access to data becomes impossible on slow connection because of their volume.
Graceful transformation is a key concept in the area of accessibility. Let's define it.
Definition:
For instance, suppose I need to check the online yellow line train schedule and I don't have visual access to the Web. If the train Web site uses a yellow wagon animated icon to point me at the schedule, and do not provide a label somewhere saying that this is for the yellow line, thus only relying on my capacity to see the color, I suddenly cannot understand this site: it does not transform gracefully.
If the DTD designer hasn't provided a way to attach alternate content to some rich piece like an animated yellow wagon, the content provider will not be able to make an accessible document.
Suppose now in a different page this Web site provides a nice clickable 2D map with all the stops and ask me to select my start and destination. If a simple list of the line stops is provided in textual form, it does transform gracefully: it's not as fast as a couple of mouse clicks, so there is some "degradation" in the system, but I can get to it.
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