Impact Analysis for Guideline 4.2

Since the tentative decision of the Working Group is to move the 
definition of the baseline out of the guidelines, we should write the 
guidelines assuming that there is a suitably accessible user agent 
available 
for content within the baseline. The guidelines should tell an author 
how to write content that will be accessible under that assumption.

We examined GL 4.2 under the above assumptions, and concluded:

- The Level 1 Success Criteria should be part of the "guidance on 
choosing a
reasonable baseline" document
- The Level 2 Success Criteron either seems to be a duplicate of the 
rest of the guidelines, or seems to be addressing user agent issues. 
We are worried that "accessibility conventions" is not well-defined. 
We recommend dropping this Success Criterion.
- At Level 3 
   - Success Criterion 1 should be part of the conformance claim, 
since we think that is the appropriate place to declare the baseline
   - Success Criterion 2 should be covered in the definition of 
baseline, so that it is clear that technologies beyond the baseline 
may be used, as long as they degrade gracefully. Techniques that 
permit graceful degredation should be described in the technology-
specific techniques
   -  Success Criterion 3 should be part of the guidance on choosing a 
reasonable
baseline

This eliminates all the success criteria for Guideline 4.2, so we 
think the Guideline should be dropped. 

We were making some assumptions about other documents, so we decided 
that we should provide proposals for those changes, as part of this 
proposal. 

We are including a proposed definition of baseline, for inclusion in 
WCAG. We will be proposing modifications to the conformance section, 
based on this definition, sometime next week. 

We are also including a proposal for guidance in how to choose a 
baseline, for inclusion in some non-normative document.


*******************************************************
 
Definition of baseline:

      The minimum set of technologies that must be supported by user 
agents
      in order to access all information and functionality of a Web 
site.
      Developers must ensure that all information and functionality of 
a
      Web site conforms to WCAG assuming user agents support only this
      minimum set of technolgies. Developers may also choose to use
      technologies that are not in the minimum set provided that the
      following are true:

         The Web site is still operable using user agents that only 
support 
         the technologies that are in the minimum set (i.e. the use of 
         technologies that are not in the minimum set does not "break" 
the 
         Web site for user agents that don't support them.)
 
         All site content and function must be available using only 
the 
         baseline technologies

*******************************************

Guide to Choosing Baselines (Non-normative)


Whether web content is accessible will depend on the User Agent(s)
available to render the web content for the user. [reference to UAAG
glossary, User agent definition] The User Agent Accessibility
Guidelines [ref] describe the requirements that will lower barriers to
accessibility.  For web content to be accessible, users need an
accessible user agent for rendering that content.

Choosing technology that is appropriate for use in accessible content
depends on knowledge of your audience and what user agents they can be
expected to have.

In some circumstances, you may have very accurate information about
your audience and may know exactly what can be assumed. For instance,
you may be developing content that will be used only within a company
where the users can be provided with the user agents that they
need. In other circumstances, you may only have statistical
information about what your audience is likely to have available. In
all cases, assume that your audience contains people with disabilities.

The capabilities of user agents change over time. Newer versions
of a user agent may meet more of the requirements of UAAG than older
versions, or they may render a wider range of technologies. The
capabilities of user agents available in different languages and
geographic regions can also vary widely.

Choosing baseline technologies is a decision based on what user
agent support you can assume in your audience at the time the baseline
is defined. When making the baseline decision, consider the following
factors.

1. How well does a user agent satisfy the requirements of UAAG for a
    technology? The proper source of this information will be a UAAG
    conformance statement for the user agent. The UAAG working group
    also lists draft information about some user agents on its web
    site.

2. What technologies does a user agent support? e.g. what version of
    HTML? of XHTML? of CSS?  of PDF? of Flash? etc. (This information 
    should be available from the user agent vendor.)

3. Which versions of assistive technology products work with the user
    agent? Which technologies are supported by the assistive
    technology, e.g., does it support JavaScript? (This information
    should be available from the assistive technology vendor.)

4. For which platforms and operating systems is a user agent available
    for a technology? Windows, Mac, Unix? Windows XP, Windows 2000, 
    Windows ME, Win98, Win 95, etc. Do operating system Service Packs 
    affect the accessibility of the user agent?

5. Is a user agent available in all the languages used by the
    audience? Is it available in the language of the content?

6. What version of a user agent is your audience using? Users don't
    always upgrade to newer versions of user agents, or may not do so
    immediately.

7. If a user agent exists, is its cost likely to be prohibitive for
    the audience, making it effectively unavailable?

8. If support for a technology by a user agent depends upon optional
    software such as a plug-in, how difficult is it for users to obtain
    the extension? Will they be prompted to install the software
    automatically if they try to use it? Do you need to provide a link
    to the plug-in as part of the content?

9. Does the technology have an open standard or a public 
specification? 

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

Received on Tuesday, 5 April 2005 23:06:28 UTC