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Re: Fw: Proposal: Canvas accessibility and a media querries approach for alternative content (Action Item 6 in the HTML Accessibility Task Force)

From: Jonas Sicking <jonas@sicking.cc>
Date: Thu, 7 Jan 2010 13:15:54 -0800
Message-ID: <63df84f1001071315n56827d4ag391311ea5c38b0bd@mail.gmail.com>
To: Richard Schwerdtfeger <schwer@us.ibm.com>
Cc: Ian Hickson <ian@hixie.ch>, public-html@w3.org, "public-canvas-api@w3.org" <public-canvas-api@w3.org>
It seems to me that the semantics of the <iframe> element more closely
matches the functionality of what you are looking for.

The <source> element currently provides alternative values for the @src
attribute of the parent element. However <canvas> has no @src attribute.

/ Jonas

On Thu, Jan 7, 2010 at 12:08 PM, Richard Schwerdtfeger <schwer@us.ibm.com>wrote:

>  Ian, others,
>
> In addition to employing a shadow DOM to produce an accessible canvas
> solution there may be situations where that approach will not be appropriate
> depending on the heavy graphics nature of canvas. In those scenarios it will
> be necessary to provide alternative content. So, we are investigating
> building off Dave Singer's media query approach to accessibility for the
> video tag.
>
> In this scenario we would need to introduce a visual media type to provide
> alternative visualization in the HTML markup whose selection would be based
> on properties defined in the Access For All standards effort. The caveat
> being the following:
>
> The HTML 5 specification defines a source element which specifies, although
> not implicitly stated, a complete file. Today much of the visual content is
> delivered as fragments and, like a mashup, we will need to pull in fragments
> for alternative content that can be used in the markup in place of canvas. A
> concrete use case would be a grid which replaces a pie chart. An entire page
> is not required for that.
>
> If it is visual content we would need to decide whether to store it in an
> IFrame in some instances:
>
> - Full pages
> - Fragments where there may be id conflicts or where security will be a
> concern
>
> Do you see any issues/concerns with:
>
> - Introducing a visual media type to HTML 5
> - expanding the specification to ensure that source fragments, for visual
> modalities, are allowed and allowing the author to specify whether the they
> be stored in an IFrame.
>
> Thanks,
>
> Rich
>
>
> Rich Schwerdtfeger
> Distinguished Engineer, SWG Accessibility Architect/Strategist
> ----- Forwarded by Richard Schwerdtfeger/Austin/IBM on 01/07/2010 11:53 AM-----
>
>
>     *Richard Schwerdtfeger/Austin/IBM@IBMUS*
>             Sent by: public-canvas-api-request@w3.org
>
>             12/15/2009 04:18 PM
>
>
> To
>
> "public-canvas-api@w3.org" <public-canvas-api@w3.org>
> cc
>
> Frank Olivier <franko@microsoft.com>, jcraig@apple.com, janina@rednote.net
> Subject
>
> Proposal: Canvas accessibility and a media querries approach for
> alternative content
> Based on feedback from David Singer and James Craig I am modifying my
> previous proposal (this is not spec. ready) to see if we can get on a
> similar page to what is being proposed for accessible media:
>
> <source media="accessibility(caption:no, audio-description:yes)"
> src="A">
>
> Here are some challenges:
>
> 1. The existing CSS 3 media queries does not support the accessibility
> properties provided. A suggestion would be to make an exception to allow the
> user agent to provide the information either internal to the browser or via
> HTML 5 local data storage. The current HTML 5 specification requires a
> direct match.
>
> 2. The source element require a source file vs. a local fragment. Should we
> consider integrating code fragment vs. entire files? If we are going to pull
> in files then they should be embedded in an IFrame in the browser for
> security reasons.
>
> 3. We need a strategy for best fit of CSS media queries for accessibility.
> We may not get a perfect match but if we can get close we should try to.
>
> With these caviats in mind here is a draft of what I am proposing that I
> would like to discuss Thursday this week:
>
> 1. The canvas element shall support zero or more child elements
> representative of the default accessible rendering (if possible) for the
> visual canvas modality and alternative modal renderings based on media types
> and accessibility properties. The media types should be based on those
> currently specified in the HTML 5 specification in addition to a subset of
> those provided in the the IMS Global Consortium Access for All Meta Data V3
> default model. The default mode would be representative of the shadow DOM.
> In many instances a more usable solution may require an alternative.
> 2. Create new media elements for canvas that support different modalities
> applicable for accessibility.
>
> Define new media elements that may be contained in canvas: called visual
>
> - default - represents a shadow DOM alternative for the default media type.
> The intent is to allow the script author to bind accessibility information
> using standard HTML elements, with ARIA semantics, to the visual rendering
> in canvas. The default element would be a child of canvas but would in no
> way be rendered by the browser. All rendering would be on the canvas through
> the use of Script provided by the author. canvas should be considered a form
> of visual media element.
>
> - visual - this is an alternative visual rendering for canvas that would be
> used if the default visual view is inaccessible based on the accessibility
> requirements requirements submitted by the author
>
> Both default and visual support aria-activedescendant where the id refers
> to a valid id in the child DOM.
>
> In the future, and as the web expands in its capability provide other media
> types such as <tactile> and <olfactory>.
>
> 3. Allow canvas to provide an audio media type as a child if the the user
> prefers an audio alternative - such as a self voicing application for a
> visually impaired user.
>
> 4. Modify the source attribute for the media attribute (included with the
> source element) as follows as defined in the Access For All version 3
> specification:
>
> 4a. adaptationtype - Provide one or more of the following adaptation types:
>
> audiodescription
> caption
> signlanguage
> highcontrast
> transcript
> alternativeText
> longDescription
> haptic
> e-book
>
> 4b. ATInteroperable - A boolean that content support interoperability with
> operating system platforms through the use of strong host language semantics
> or the use of WAI-ARIA for web content. If a plug-in is provided (say a Java
> applet) the application must support interoperability through the use of a
> recognized Accessibility API.
>
> 4c. languageOfAdaptation - value determined by [ISO 639-2:1998]
>
> 4d. EducationLevelOfAdaptiaon - Define a range based on the adapation
> (Integer)
>
> 4e. ControlFlexibility: Provide one or more of fullKeyboardControl,
> fullMouseControl
>
> 5e. DisplayTranformability:One or more of the following:
>
> fontSize
> fontFace
> fontWeight
> letterSpacing
> wordSpacing
> lineHeight
> foregroundColour
> backgroundColour
> cursorPresentation
> highlightPresentation
> layout
> structurePresentation
>
> 6e. Harzard: One ore more of the following:
>
> flashing, sound, olfactory, motionSimulation
>
>
> We can use a subset of these.
>
> 5. View Selection should be based on a user preference in the browser based
> on the mode and type preference supported in HTML 5. If nothing is set, the
> shadow DOM is used for the accessibility mapping when provided. The user
> agent should select the first view that fits the user's request. Platform
> accessibility API may also be used to configure the view selection. Note: is
> no alternative view is provided to meet the preferences the view reverts
> back to the canvas + shadow DOM view. The shadow DOM is also optional.
>
> 6. The canvas tag shall include a script method to set the bounding
> rectangle for a given valid id in the shadow DOM. This would allow
> the browser to provide the bounding rectangle for the id in the shadow DOM
> when it receives focus. The rectangle should be relative to the location of
> the canvas element and would be converted to screen coordinates in the
> accessibility API and would allow the canvas to move without changing the
> location of the shadow DOM element. This will allow screen magnifiers to
> determine the visible focus. (Ideally it would be nice to also do this via
> XPath statements vs. id)
> 7. All allowable HTML elements in the shadow DOM shall support the tabindex
> content attribute and ARIA attributes.
> 8. The shadow DOM should include all renderable HTML elements save standard
> input controls. The reasoning being is these
> controls are user agent managed in terms of the keyboard and would likely
> conflict with canvas keyboard management.
>
>
> The format would look something along the following lines:
> <canvas>
>  <default aria-activedescendant="foo">  /*Since canvas is visual this is
> the default mode. It contains the shadow DOM*/
>     <div role="toolbar">
>        <div role="tab" tabindex="-1" id="foo">
>        </div>
>     </div>
>  </access>
>  <visual type="text"> /*Here we could place a long description or an
> alternative aria-enabled widget*/
>  </access>
>  <audio>
>  </access>
>  <tactile> /*This is in access for all and we could lose it for now for
> obvious reasons*/
>  </access>
>  <olfactory> /*This is in access for all and we could lose it for now for
> obvious reasons*/
>  </access>
>  <visual type="signlanguage">
>  </access>
> </canvas>
>
>
> Rich Schwerdtfeger
> Distinguished Engineer, SWG Accessibility Architect/Strategist
>


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Received on Thursday, 7 January 2010 21:16:51 UTC

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