ERCIM News No.41 - April 2000 [contents]

XML Accessibility Guidelines

by Daniel Dardailler

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 guarantee of device independence or textual alternate support. In this context, guidelines are needed that explain XML formats and tools designers how to include basic accessibility features - such as the ones present in HTML - in all their new development.

XML (Extensible Markup Language) is a meta-syntax, used to create new languages. It can be seen as a simplification 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 (Hypertext 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 documents like:

<TITLE> XML and Accessibility </TITLE>
<BODY> <ADDRESS lang=fr> Daniel Dardailler </ADDRESS>

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 Chowder
<PHOTO url="clam.jpg">A large creamy bowl of clam showder, with bread crumbs on top</PHOTO>

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).

Problem statement

The Web Accessibility Initiative (WAI) has done extensive work in the HTML area, resulting in lots of new functionalities being added to the version 4.0 of the language. 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 pervasive presence and widely available specification. For instance, one can design a set of XML tags that would prevent the creation of accessible document, such as:

<MENU>New England Restaurant </MENU>
<APPETIZER>Clam Chowder
<PHOTO url="clam.jpg"/>

with no way to include an alternate textual description of the photo, for instance.

But let’s start by defining what we mean by accessible DTD and documents. 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. For User-centric XML based languages, 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 semantic 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 seamless access (ie, you don’t need a programmer, you just need a program).

Guidelines for Designers of User Interface-oriented XML Tagset

This section provides a list of proposed 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.

1. Ensure that authors can associate a text description with any non-text content (graphics, sound, multimedia, scripts, etc.):

2. Create semantically-rich languages. Do not define presentation elements or attributes:

3. Export semantics:

4. design an accessible user interface:

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 Scalable Vector Graphics (SVG) specification for an example of both practices (http://www.w3.org/Graphics/SVG/).


Our primary message is simple: be device independent, and export your semantics as much as you can. We believe abstract guidelines and verifiable checkpoints/ techniques (using implementation mechanisms associated with abstract guidelines) are the best way to address this problem and we are in process of defining them in the framework of the WAI at W3C.

WAI: http://www.w3.org/WAI
WAI and XML: http://www.w3.org/WAI/PF/xmlgl

Please contact: 

Daniel Dardailler - W3C
Tel: +33 4 9238 7983
E-mail: danield@w3.org