Questions and Answers about Baseline and WCAG 2.0

Page Contents

Background=20
What is a baseline?=20
Who sets the baseline?=20
How can we be sure a site is accessible?=20
Help for developers?=20
Other aids for developers?=20
Why wasn't UAAG used?=20
In Closing=20
Additional Information

Background

The World Wide Web has evolved considerably since the release of the = WCAG 1.0=20 in 1999. The WCAG 1.0 was written assuming that Web users would = primarily be=20 using HTML. Today, the Web is used in hundreds of ways that were not = possible in=20 1999. Many new Web technologies are emerging and existing technologies = are=20 becoming more comprehensive as the Web community finds new and original = ways to=20 disseminate information and interact with it. Also, due to language, = economic=20 differences and other factors, technologies that are common in one part = of the=20 world may not be present, or may not be as up to date, in others

Given these realities, the WCAG working group realized that it would = have to=20 find a different basis upon which to form version 2.0 of the guidelines. = It=20 would have to present Web accessibility as a set of principles that = would work=20 across all of today's technologies and that would be robust enough to = withstand=20 dramatic shifts and changes in technology. The WCAG 2.0 would have to = apply to a=20 wide range of W3C and non-W3C technologies. It would need to be a = document that=20 would give policy makers and managers guidance about what outcomes are = necessary=20 when striving to create accessible Web content, yet allow for = differences=20 between technologies and cultures without introducing guidelines that = are=20 incompatible between countries.

To address these needs, the working group has developed a set of = guidelines=20 and success criteria that are technology independent. These are = presented in the=20 document, Web Content = Accessibility=20 Guidelines 2.0. This guideline document is accompanied by an = informative=20 document called Understanding WCAG 2.0 that provides examples and lists = of=20 techniques that are sufficient to meet the success criteria in WCAG 2.0. = This=20 two-layered approach makes it possible to have stable criteria for = accessibility=20 with supporting technical documents that can be updated as the = technologies=20 evolve and new ways of satisfying the success criteria are developed. =

A key element in this model is the ability to define the set of = technologies=20 that user agents can be assumed to support. As new technologies come out = it is=20 not necessarily a valid assumption that user agents including assistive=20 technologies will be able to support them all on the day they are = announced.=20 Some mechanism defining the technologies that can be assumed to be = enabled and=20 working in user agents (including AT) is needed. The group, however, = found that=20 choosing any set of technologies and defining it in WCAG (overtly or = through the=20 definition of the success criteria) would quickly date the new = guidelines, as=20 the previous (WCAG 1.0) guidelines had become dated. It would limit the = ability=20 of Web content that is accessible in the future, using future = technologies, to=20 claim conformance using those new technologies.

After trying to solve the problem several times in this manner = (including=20 trying to use the User Agent Accessibility Guidelines 1.0 to define the = set of=20 technologies; see below), the working group determined that the only way = to=20 solve the problem was to introduce a new concept: "baseline".

Note: Although UAAG 1.0 does not provide the baseline for WCAG = 2.0 for=20 the reasons discussed above, UAAG is useful in assessing the = accessibility of=20 user agents when trying to decide if a technology being considered for = inclusion=20 in a baseline is supported by accessible user agents. User agents that = conform=20 to UAAG 1.0 will also provide better support for Web content that = conforms to=20 WCAG 2.0.

What is a baseline?

A "baseline" (as used in WCAG 2.0) is the set of such technologies = that an=20 author assumes are supported and turned on in accessible user agents. = Authors=20 must ensure that all information and functionality of the Web content = conforms=20 to WCAG 2.0 assuming that user agents support only of the technologies = in the=20 baseline (and have them enabled).

The Baseline may be set by the author or another individual, or = organization=20 or a governmental body. When authors make WCAG 2.0 conformance claims, = they must=20 specify the Baseline that they are using to make that claim. In making = their=20 claim they are then claiming that the content will meet WCAG 2.0 at the = stated=20 level of conformance if a user agent can support the technologies listed = in the=20 baseline. When baselines are set by someone else, authors may actually = rely on=20 only some of the technologies in the baseline (a subset of them).

Non-baseline technologies can also be used, but all information and=20 functionality of the Web content must conform both with all non-baseline = technologies turned on and with the non-baseline technologies turned = off. Both=20 conditions are necessary since some users many have browsers that = support them=20 while others may not.

Examples of Baselines (and what they mean) include

Example 1 Baseline: HTML 4.01 Transitional, .GIF, and .JPEG

A claim using this baseline means that, if the user agent supports = these=20 technologies, the content satisfies all success criteria for the = conformance=20 level claimed by the author.

This baseline allows any content that can be created in HTML 4.01, in = addition to .GIF and .JPEG images, the most widely used image formats = today.=20 This extremely limited baseline might be appropriate for content aimed = at a very=20 broad audience when there is little or no specific knowledge about what = user=20 agents are available to that audience. Authors using this baseline may = rely upon=20 these technologies, and may use the HTML 4.01 techniques described as=20 =E2=80=9Csufficient=E2=80=9D in Understanding WCAG 2.0. (Authors may = further enhance the user=20 experience by also using additional HTML techniques listed as = =E2=80=9Cadvisory=E2=80=9D=20 (optional) in Understanding WCAG 2.0.)

Example 2 Baseline: HTML 4.01 Transitional, CSS, GIF, JPEG, and=20 JavaScript.

Consider the scenario of a Web site that provides a list of = =E2=80=9Cquick links=E2=80=9D for=20 navigating to frequently accessed sections of the site. SC 3.2.2 = requires that=20 changing the setting of any form control or field does not automatically = cause a=20 change of context (beyond moving to the next field in tab order) unless = the=20 delivery unit contains instructions before the control that describe the = behavior. If JavaScript were listed in the baseline, the script = techniques=20 listed as =E2=80=9Csufficient=E2=80=9D in Understanding WCAG 2.0 could = be relied upon to produce=20 conforming content, and it would not be necessary to provide = alternatives that=20 work when JavaScript is disabled. In the case of SC 3.2.2, this would = mean that=20 the script technique =E2=80=9CHiding and showing content based upon a = select element=20 change=E2=80=9D together with the general technique =E2=80=9CProviding a = submit button to=20 initiate a change of context=E2=80=9D would be sufficient.

JavaScript is not listed in Sample Baseline 1, however, so using this = script=20 technique would not be sufficient for the Baseline in example1. Instead, = the=20 HTML technique =E2=80=9CProviding submit buttons in HTML=E2=80=9D = together with the general=20 technique =E2=80=9CProviding a submit button to initiate a change of = context=E2=80=9D would be=20 sufficient. JavaScript might still be used within the Web unit for other = purposes, but accessible alternatives that do not rely on JavaScript = would be=20 required.

Here we can see how the baseline concept works. In environments where = it is=20 save to assume that people=E2=80=99s user agents (including assistive = technologies) will=20 all support JavaScript, it would be appropriate to use Example 2 = Baseline.=20 If people=E2=80=99s user agents (and AT) cannot be counted = on to support=20 JavaScript, then the Example 1 Baseline would be the only appropriate = one to=20 specify.

Example 3 Baseline: HTML 4.01 Transitional, CSS, GIF, JPEG, MOV, AVI = class=3DGramE>, MP3, RM, RT

Sample Baseline 1 does not include multimedia technologies such as = audio and=20 video. What happens if the Web unit includes multimedia?

Since audio and video formats are not listed in Example Baseline 1, = these=20 technologies may be used, but not relied upon=20 style=3D'mso-bidi-font-style:italic'> (for Sample Baseline 1 content) = because=20 it cannot be assumed that users have accessible media players. If a Web = page=20 does use multimedia, an alternative version of the content that = relies=20 only upon technologies in the baseline must be available from the same = page as=20 the multimedia=E2=80=94even if captions and audio descriptions are = available for the=20 multimedia. The alternate version must provide all of the same = information and=20 functionality as the multimedia, and it must be updated whenever the = multimedia=20 content is updated (as required by SC 4.2.1).

However =E2=80=93 with Sample Baseline 2 the author could rely = on the=20 multimedia access features. So a movie with captions and = audio=20 descriptions would be sufficient for level 1 conformance. = It would=20 not be necessary to provide all the information in another accessible = format.=20

Baseline specifications are not browser specifications

The baseline is not the same as statements such as "this Web content = works=20 best using IE 6.0". This would be an invalid baseline statement. The = baseline=20 cannot be browser or user agent specific. It is a set of technologies. = There is=20 a subtle but important distinction. The types of technology to be listed = in the=20 baseline include but are not limited to:

Markup languages (including but not limited to XHTML, XML, SMIL, = SVG,=20 MathML, etc.);=20
Programming languages (such as Java and including but not limited = to=20 scripting languages such as JavaScript);=20
Style sheets (including but not limited to style sheet languages = such as=20 CSS, XSL, and XSLT);=20
Data formats (including but not limited to image formats, video = formats,=20 audio formats, and document formats); and=20
APIs (Application Programming Interfaces, including but not = limited to=20 Microsoft Active Accessibility and the Java Accessibility API). =

These are classes of technology used to create content or make it = available=20 to users via the user agent. A baseline, then, is a list of specific=20 technologies that belong to the classes above.

One reason it is important to be technology-specific rather than user = agent=20 specific is that restricting users to specific user agents may pose=20 insurmountable accessibility problems for some people. It would be = almost=20 impossible to know all of these problems in advance unless perhaps the = content=20 was to be used in a closed environment.

Baselines are not about audience abilities

The baseline statement is also not a statement about what physical, = sensory=20 or cognitive abilities are required to use content. It is a = technology-specific=20 statement about what technologies a user agent must support for the = content to=20 be accessible at the claimed level.

One assumption that must be made by all stakeholders who are creating = Web=20 content is that the target audience will include people with = disabilities.=20 People with disabilities are to be considered an integral part of all=20 demographics. One cannot exclude people with disabilities from the = target=20 audience.

Using baselines in conformance claims

In claiming conformance to WCAG 2.0, developers are claiming that all = information and functionality of the Web content conforms to WCAG 2.0 at = a given=20 level if the user agent supports the stated baseline technologies.

Over time, the baselines used by various organizations and = governments may=20 change to accommodate new technological advances. The intention of the = WCAG 2.0=20 is that the principles and functional outcomes of the guidelines remain = stable=20 during technological change because they are both technology independent = and=20 baseline independent.

Who sets the baseline?

Although there was no mention of a baseline in the 1999 WCAG 1.0 = Guidelines,=20 there was an implicit baseline used for those guidelines. Simply put, = the WCAG=20 1.0 assumed a baseline of HTML, and a few graphic and media = technologies. In=20 this respect, a baseline was assumed and was "hard wired" into the=20 specifications. Since WCAG 1.0 was written with HTML in mind, a baseline = was set=20 by and included in the guidelines themselves. The constraints this = presented=20 were a key reason for the need for WCAG 2.0.

In the WCAG 2.0 Guidelines, no particular baseline is assumed. = Instead the=20 baseline is assumed to be set outside of the WCAG 2.0 document. The = baseline may=20 be set by any one of a number of sources.

Government or corporate policy may decide what = technologies=20 are in the baseline.=20
A baseline could be set by a customer that would require = certain=20 technologies and features.=20
The organization that employs the author might set the = baseline to=20 be used.=20
If no one else above the developer sets the baseline, then the=20 author would set it.

The WAI may provide guidance in setting baselines, but is not setting = "The=20 Baseline" or "A Baseline" for WCAG 2.0. The sample baselines discussed = above are=20 just that: samples. They do not represent baselines recommended by the = WCAG=20 Working Group, the WAI, or the W3C.

If the WCAG does not set the = baseline, then=20 how can we be sure that a site will be accessible?

No site or content is ever completely accessible.

Conformance to WCAG 2.0 at some level provides that level of = accessibility=20 for users whose agents can support the stated baseline technologies for = that=20 content.

If developers choose a baseline that is too high, that includes too = many=20 technologies that are not supported by user agents in use by people with = disabilities, then those sites or that content may not be accessible to = those=20 people. It is up to developers to use baselines that are reasonable and=20 appropriate to the times and the technical levels of user agents of = people with=20 disabilities.

If developers do not use reasonable baselines, then it is up to = companies,=20 customers or regulatory agencies to set baselines that are appropriate = for the=20 time and possibly for different types of content (e.g. public = information vs.=20 internal content) or environments (Worldwide Web vs. Intranet).

What is available to help = developers choose=20 a baseline?

There is an informative document called =E2=80=9CHow to Meet SC = x.x.x=E2=80=9D for each=20 success criterion. This "How to Meet" document provides important = information=20 about the success criterion, including definitions of key terms (also = available=20 in the normative Glossary), an explanation of the intent of the success=20 criterion, and a list of sufficient and optional techniques as well as = common=20 failures. The =E2=80=9CHow to Meet=E2=80=9D document also shows who = benefits from the success=20 criterion, and lists examples and related resources for further = information for=20 that WCAG 2.0 success criterion. In addition, the individual technique = documents=20 have a section titled =E2=80=9CUser Agent and Assistive Technology = Support Notes=E2=80=9D where=20 appropriate that provides information on the support for different = techniques or=20 technologies by assistive technologies.

The W3C-WAI may also prepare "A Guide for Policy Makers" to help=20 organizations choose a baseline that will ensure the maximum = accessibility for=20 their environments. There may also be resources that describe what user = agent=20 support is available in different languages and different geographies. =

What other aids will = be available=20 for developers?

W3C technologies

The WCAG will provide technology-specific techniques documents for = various=20 W3C technologies. Where the "How to meet..." documents describe = sufficient ways=20 to meet each success criterion of the guidelines, the technique = documents will=20 provide detail on both sufficient and advisory techniques including = examples,=20 code, and test procedures where appropriate.

Non-W3C technologies

W3C is not in a position to create guidance documents for = technologies not=20 developed by the W3C. However, W3C is working with vendors to develop = similar=20 materials.

Most major non-W3C technology providers are in the process of = developing=20 accessibility techniques that will help users of their technologies meet = the=20 WCAG guidelines. Just as with W3C technologies, in order to claim = conformance,=20 any content using these technologies will have to meet all of the level = 1 WCAG=20 2.0 success criteria.

For non-W3C technologies that do not have their own techniques = documents, the=20 functional outcomes described in the success criterion can be used to = evaluate=20 content for accessibility at the three WCAG 2.0 levels of conformance. =

Why wasn't UAAG used as = Baseline?

The User Agent Accessibility Guidelines 1.0 (UAAG) will provide = helpful=20 direction to stakeholders who are choosing a baseline. It was a serious=20 consideration of the working group to use the UAAG as the WCAG 2.0 = baseline. In=20 fact, the working group tried to do that at one point. However, after = careful=20 consideration and much effort and research, it was determined that the = UAAG=20 would not be a workable baseline for the WCAG for many reasons including = the=20 following:

The Baseline is about technologies =E2=80=94 not user agents. So = UAAG must be=20 transformed from user agent specifications to technologies used by = user=20 agents. This was complicated but not insurmountable.=20
Many of the UAAG specifications do not actually require support = for=20 technologies or capabilities in the User Agent; they just provide=20 specifications for what should be true if they are supported. Thus, = much of=20 the guidance was optional.=20
Today, there are no user agents that fully conform to UAAG = (support all=20 the technologies in the way specified in UAAG).=20
The WCAG would have to recommend repair techniques that compensate = for=20 User Agents that do not conform to UAAG, which could create confusion = about=20 what conformance means.=20
UAAG does not answer key questions about how Assistive Technology=20 capabilities interact with user agent capabilities =E2=80=94 yet AT is = an essential=20 part of the user agent for many people with disabilities.=20
There are financial and language considerations, that are outside = the=20 scope of the UAAG. Many capabilities assumed by UAAG do not exist in = many=20 languages.=20
Using the UAAG as the baseline could mean a baseline that would = only be=20 met by the most popularly supported Assistive Technologies which are = only=20 available in some languages.

Note: Although UAAG 1.0 does not provide the baseline for WCAG = 2.0 for=20 the reasons discussed above, UAAG is useful in assessing the = accessibility of=20 user agents when trying to decide if a technology being considered for = inclusion=20 in a baseline is supported by accessible user agents. User agents that = conform=20 to UAAG 1.0 will also provide better support for Web content that = conforms to=20 WCAG 2.0.

In Closing

The technological environment of today is vastly different from that = of 1999=20 when the WCAG 1.0 was released. We need to respond to these new = realities in a=20 way that will empower people with disabilities in this new environment = while=20 facilitating effective technological innovation, communication, and = commerce on=20 the Web. The baseline concept is a proposed response to these = challenges. It=20 also reflects our experience of watching the implementation of the WCAG = 1.0 over=20 the past number of years. We seek comments and suggestions and welcome = your=20 input.

Additional = Information=20 Related to Baseline and Conformance

Use of baselines within a conformance statement

A conformance claim includes the following assertions:

Required components of a conformance Claim

Conformance claims are not required. However, if you make a = conformance claim=20 then the conformance claim must include the following=20 assertions:

The date of the claim.=20
The guidelines title/version: "Web Content Accessibility = Guidelines 2.0".=20
The URI of the guidelines: http://www.w3.org= /TR/2005/REC-WCAG20-YYYYMMDD/.=20
The conformance level satisfied: (Level 1, 2 or 3).=20
The Baseline used to make the conformance claim. (If baseline is a = published baseline it can be named along with a URI that points to it. = The=20 baseline technologies can also be spelled out individually in the = conformance=20 claim. )=20
Scope of the claim (a URI, list of URI's or a regular expression). =

Optional components of a conformance Claim

A list of the specific technologies "relied upon" to create the = content=20 for which the claim is being made.=20
- "Technologies" includes markup languages, style sheet languages, = scripting/programming languages, image formats, and multimedia = formats.=20
- "Relied upon" means that the content would not meet WCAG 2.0 at = the=20 claimed level if that technology is turned off or not supported.=20
- The set of "Relied Upon" technologies must be a proper subset of = the=20 Baseline.
A list of the specific technologies that are "used" but not = "relied upon".=20
- If a technology is "used" but not "relied upon" the content = would still=20 meet WCAG 2.0 at the stated conformance level even if that = technology is=20 turned off or not supported.
A list of user agents that the content has been tested on. This = should=20 include assistive technologies.=20
Information about audience assumptions or target audience. This = could=20 include language, geographic information. It CANNOT specify physical, = sensory=20 or cognitive requirements.

Examples of conformance claims

Example 1

On 23 March 2005, http://www.wondercall.example.com conforms to W3C's = WCAG=20 2.0, Conformance Level A The baseline for this claim is XHTML 1.0. The=20 specification that this content "relies upon" is: HTML = 4.01.=20 The specifications that this content "uses but does not rely=20 on" are: CSS2, and gif. This content was tested using the = following=20 user agents and assistive technologies: Firefox 1.5 on Windows 2000 SP4 = with=20 Jaws 7.0, Firefox 1.5 on Windows XP SP 2 with Jaws 7.0, IE 6.0 on = Windows 2000=20 SP4 with Jaws 4.51, IE 6.0 on Windows 2000 SP4 with Jaws 7.0, and = Firefox 1.5 on=20 Windows XP SP2 with Jaws 7.0, Safari 2.0 with OS X 10.4

Example 2

On 5 May 2006, "G7: An Introduction"=20 http://telcor.example.com/nav/G7/intro.html conforms to W3C's WCAG 2.0.=20 class=3DGramE> class=3Dgrame>Conformance Level Double-A. The = following=20 additional success criteria have also been met: 1.1.2, 1.2.5, and 1.4.3. = The=20 baseline for this claim is UDBaseline#1-2006 at=20 http://UDLabs.org/Baseline#1-2006.html. The specification that this = content=20 "relies upon" is: XHTML 1.0 (Strict), and Real Video. = The=20 specifications that this content "uses but does not rely = on"=20 are: JavaScript 1.2, CSS2.

Example 3

On 21 June 2007, http://example.com/nav and http://example.com/docs = conform=20 to W3C's WCAG 2.0, Conformance Triple-A. The baseline is = ISA-Baseline#2-2007 at=20 http://ISA.example.gov/Baselines/BL2-2007. The specifications that this = content=20 "relies upon" are: XHTML 1.0 (Strict), CSS2, JavaScript = 1.2,=20 jpeg, class=3Dspelle>png. class=3DGramE> class=3Dgrame>" The = technologies=20 this content has been tested with can be found at=20 http://example.com/docs/WCAG20/test/technologies.html.

Vertical and Horizontal Scoping in Conformance Statements

Question

"Can content conform to the WCAG 2.0 except for a section where = people post=20 information and class=3DGramE>files. We cannot always be sure they = will post=20 conforming content. What do we do?"

Answer

Authors cannot claim conformance for any section of web content that = cannot=20 be guaranteed to conform to the guidelines. One common place this might = occur is=20 public forums where organizations may not have complete control over = what is=20 posted to their content.

To handle this and similar situations WCAG 2.0 includes the concept = of=20 scoping. A conformance claim may scope out" specific sections of a site. = This is=20 "vertical scoping" (scoping out a portion of a site by URI or URI range) = and is=20 allowed. WCAG 2.0 conformance can be claimed for any portions of a site = and/or=20 can claim all but certain sections of the site.

"Horizontal scoping" (scoping out a particular technology within Web = units)=20 is not allowed. A company could not say something like "our content = conforms to=20 the WCAG 2.0 at level 1 except all the navigation menus are not = compliant," or,=20 "our content conforms except for all the multimedia and animations." = This would=20 be scoping out parts of various Web units and would not be a valid or = acceptable=20 WCAG 2.0 conformance claim. Any Web content (Web unit or set of Web = units) that=20 is part of a conformance claim at Level A or Level AA must meet all of = the=20 Success criteria for the level or levels that it claims Any Web content = for=20 which Level AAA conformance is claimed must meet all Level 1 and Level 2 = success=20 criteria plus 50% of applicable Level 3 success criteria..

Examples of People and Places Setting Baselines

Example 1: A government site that provides information to = the=20 public
A government agency publishes information intended = for the=20 general public. The specified baseline includes only technologies that = have=20 been widely supported by more than one accessible and affordable user = agent=20 for more than one release. The government periodically changes the = baseline it=20 requires for authors of public sites to reflect the increasing ability = of=20 affordable user agents (including assistive technology) to work with = newer=20 technologies.=20
Example 2: A particular government provides high level = accessible=20 user agents to all citizens who need them.
A government = provides=20 all citizens with user agents that support newer technologies. The = government=20 is thus able to specify a baseline that includes these newer = technologies for=20 all of its Web sites for its citizens since the government can assume = its=20 citizens' user agents can handle the technologies..=20
Example 3: A private intranet.
An = organization=20 (public or private) provides its employees with the information = technology=20 tools they need to do their jobs. The baseline for intranet sites used = only by=20 employees includes newer technologies that are supported only by the = user=20 agent that the organization provides for its employees. Because the = company=20 controls the user agents that will view its internal content, the = author has a=20 very accurate knowledge of the technologies that those user agents = (including=20 assistive technologies) support.

Note that baselines are not specified in terms of specific user = agents but=20 rather in terms of the Web content technologies that are supported and = enabled=20 in those user agents (including assistive technologies)

Some initial guidance in choosing a baseline

Choosing baseline = technologies=20 is a decision based on what technologies you can assume are supported by = the=20 user agents of your audience at the time the baseline is defined. When = making=20 the baseline decision, consider the following factors.

INTRANET

If you are in a closed environment (Intranet) where the user agents = used are=20 controlled and the Assistive Technology needed to make that user agent=20 accessible are known, then you can set a baseline that is tuned to the=20 capabilities of that user agent. Some questions to ask about that user = agent=20 (and AT combination).

How well does the user agent satisfy the requirements of UAAG for = each=20 technology being considered? A source of this information will be the = UAAG=20 conformance statement for the user agent. The UAAG working group also = lists=20 draft information about some user agents on its Web site.=20
>What technologies does the user agent support? For example, = what=20 version of HTML, XHTML, CSS, PDF, Flash etc.? (This information should = be=20 available from the user agent vendor.)=20
Which versions of assistive technology products work with the user = agent?=20 And which technologies are supported by the assistive technology, = e.g., does=20 it support JavaScript? (This information should be available from the=20 assistive technology vendor.)

NOTE: Care must be taken when making assumptions about which = assistive=20 technologies will be used in a company.

INTERNET

Most Web content is designed to be posted on the World Wide Web. For = this=20 content it is not possible to know what platform or user agent people = will be=20 using. It may be any one of many user agents running on any one of a = number of=20 operating systems (Windows, Macintosh, Unix, Windows XP, Windows 2000, = Windows=20 ME, Windows 98, Windows 95). Sometimes service packs can make a = difference. When=20 dealing with the Internet, it is therefore important to think in terms = of=20 technologies and not browsers.

Below are some question to consider.

For which platforms and operating systems is a user agent = available for=20 each technology being considered? Windows, Mac, Unix? Windows XP, = Windows=20 2000, Windows ME, Windows 98, Windows 95, etc. Do operating system = Service=20 Packs affect the accessibility of the user agent?=20
Is each candidate technology supported by a user agent (if one = exists) in=20 all the languages used by the audience? Is it available in the = language of the=20 content?=20
Is each candidate technology supported by recent versions of a = user agent=20 your audience is using? Users do not always upgrade to newer versions = of user=20 agents, or may not do so immediately..=20
Is each candidate technology supported only by user agents that = are very=20 expensive so that the cost is likely to be prohibitive for the = audience,=20 making it effectively unavailable?=20
If support for a technology by a user agent depends upon optional = software=20 such as a plug-in, how difficult is it for users to obtain the plug = in? Will=20 they be prompted to install the software automatically if they try to = use it?=20 Is the accessible version of the plug-in different from the one that = is=20 usually downloaded or pointed to? Do you need to provide a link to the = accessible version of the plug-in as part of the content?=20
Does the technology have an open standard or a public = specification?=20

An appropriate baseline for accessible Web content will make a = conservative=20 choice to ensure that users will have accessible user agents for = rendering the=20 Web content. However, this does not prohibit the use of other = technologies, as=20 long as they are used in such a way that user agents that support only = the=20 technologies in the baseline can still render the content = accessibly.

Glossary

See Glossary in WCAG 2.0 at http://www.w3.org/TR/WCAG20 =

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