Your comments on WCAG 2.0 Last Call Draft of April 2006

Dear Chris Lilley ,

Thank you for your comments on the 2006 Last Call Working Draft of the
Web Content Accessibility Guidelines 2.0 (WCAG 2.0
http://www.w3.org/TR/2006/WD-WCAG20-20060427/). We appreciate the
interest that you have taken in these guidelines.

We apologize for the delay in getting back to you. We received many
constructive comments, and sometimes addressing one issue would cause
us to revise wording covered by an earlier issue. We therefore waited
until all comments had been addressed before responding to commenters.

This message contains the comments you submitted and the resolutions
to your comments. Each comment includes a link to the archived copy of
your original comment on
http://lists.w3.org/Archives/Public/public-comments-wcag20/, and may
also include links to the relevant changes in the updated WCAG 2.0
Public Working Draft at http://www.w3.org/TR/2007/WD-WCAG20-20070517/.

PLEASE REVIEW the decisions  for the following comments and reply to
us by 7 June at public-comments-WCAG20@w3.org to say whether you are
satisfied with the decision taken. Note that this list is publicly
archived.

We also welcome your comments on the rest of the updated WCAG 2.0
Public Working Draft by 29 June 2007. We have revised the guidelines
and the accompanying documents substantially. A detailed summary of
issues, revisions, and rationales for changes is at
http://www.w3.org/WAI/GL/2007/05/change-summary.html . Please see
http://www.w3.org/WAI/ for more information about the current review.

Thank you,

Loretta Guarino Reid, WCAG WG Co-Chair
Gregg Vanderheiden, WCAG WG Co-Chair
Michael Cooper, WCAG WG Staff Contact

On behalf of the WCAG Working Group

----------------------------------------------------------
Comment 1:

Source: http://www.w3.org/mid/20060522154433.CF78166363@dolph.w3.org
(Issue ID: LC-580)

Part of Item:
Comment Type: TE
Comment (including rationale for proposed change):

The term "luminosity" is incorrect here (it applies only to certain
Broadcast video signals). Relative luninance is the correct term. When
used as a ratio, the difference between absolute and relative
Luminance can be dropped, but the term luminance rather than
luminosity should be used.

http://www.w3.org/TR/2006/WD-WCAG20-20060427/appendixA.html#luminosity-contrastdef
defines the coefficients for calculating luminance, and its good to
see that the Rec.709 chromaticities are used (rather than, for
example, the NTSC ones which do not apply to modern computer monitors
at all). (the coeeficients are correct, see the "luminanceToAlpha"
section of http://www.w3.org/TR/SVG11/filters.html#feColorMatrix but
the specification does not explain why this is so.

However the text as it stands implies that the formula given is
universally applicable. it is not. This is particularly importnt when
printing Web materials.

Proposed Change:

change "luminosity" to luminance throughout.

change "The luminosity of a color is defined as" to "the luminance of
an sRGB color is defined as".

change "blue RGB values" to "blue sRGB values" (the equation does not
apply to other color spaces).

Remove the exponentiation operator and the 2.2 gamma approximation.
Instead, use the correct sRGB transfer curve.

Reference the sRGB specification. See the SVG 1.2Tiny specification
for an example of how to reference it.

You may want to note that the equation given is only correct for
typicalcolor vision (the ISO standard observer). For atypical color
vision, often incorrectly termed color blindness, different equations
apply depending on the type of  atypical color vision and the degree
of severity.
For more information, please see
http://www.w3.org/Graphics/atypical-color-response

----------------------------
Response from Working Group:
----------------------------

Thanks for the comments and suggestions.  To take them each in turn:

CL: change "luminosity" to luminance throughout.
Since Web content doesn't provide any light output (HTML doesn't give
off photons) we can't use the word "luminance" (which means light
output).  However 'relative luminance' is used in the literature for
the concept we are describing and we are now using this.

CL: change "The luminosity of a color is defined as" to "the luminance
of an sRGB color is defined as".

See above regarding luminance. And, we have switched to specifying
that we are talking about sRGB in our equations.

CL: change "blue RGB values" to "blue sRGB values" (the equation does
not apply to other color spaces).

Correct and we have done so.

CL: Remove the exponentiation operator and the 2.2 gamma
approximation. Instead, use the correct sRGB transfer curve.

Done.  Now uses the equations from the W3C document on sRGB.

CL: Reference the sRGB specification. See the SVG 1.2Tiny
specification for an example of how to reference it.

Done

CL: You may want to note that the equation given is only correct for
typical color vision (the ISO standard observer). For atypical color
vision, often incorrectly termed color blindness, different equations
apply depending on the type of atypical color vision and the degree of
severity. For more information, please see
http://www.w3.org/Graphics/atypical-color-response.

We have explained this briefly in our "Understanding" document. A
longer exposition of this will be released in a paper (since it is too
complicated to put into How to Meet SC 1.4.3 itself. The contrast
ratios were set higher than normal and in a way to account for low
vision and  atypical color vision.

The paper "Atypical colour response" has also been added as a resource.

You can find the updated SC and definitions at
http://www.w3.org/TR/2007/WD-WCAG20-20070517/#visual-audio-contrast-contrast
and http://www.w3.org/TR/2007/WD-WCAG20-20070517/#visual-audio-contrast7
.

The Understanding SC 1.4.3 and 1.4.5 documents can be found at
http://www.w3.org/TR/2007/WD-UNDERSTANDING-WCAG20-20070517/#visual-audio-contrast-contrast
and http://www.w3.org/TR/2007/WD-UNDERSTANDING-WCAG20-20070517/#visual-audio-contrast7
.

----------------------------------------------------------
Comment 2:

Source: http://www.w3.org/mid/20060522155848.9BF2ADAE7D@w3c4-bis.w3.org
(Issue ID: LC-581)

Part of Item:
Comment Type: TE
Comment (including rationale for proposed change):

"3.2.2  Changing the setting of any form control or field does not
automatically cause a change of context (beyond moving to the next
field in tab order), unless the authored unit contains instructions
before the control that describe the behavior"

Consider a user interface for a map, where form fields such as panning
controls, layer selections or search boxes are used to zoom,pan, or
alter a map. This common use seems to be precluded by the text above.

Proposed Change:

I regret not being able to suggest suitable text at this time. I can
see the benefit of what you are trying to do, and I can see that it
makes non-confomant some interfaces that are currently used. I think
the text needs to be more precise, and look forward to discussing this
further with you.

----------------------------
Response from Working Group:
----------------------------

User interfaces that allow the user to select different views of the
same data cause changes in content, but not changes in context.
Success Criterion 4.1.2 has been changed to require that user agents
and assistive technology be notified of the changes in state produced
by such changes in views.

Received on Thursday, 17 May 2007 23:29:27 UTC