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Re: Systematic approach to layout table heuristics

From: James Craig <jcraig@apple.com>
Date: Fri, 21 Feb 2014 10:29:36 -0800
Cc: HTML Accessibility Task Force <public-html-a11y@w3.org>
Message-id: <28A67A6C-6E30-4303-A4E1-53C3C3D39C69@apple.com>
To: Leif Halvard Silli <xn--mlform-iua@xn--mlform-iua.no>
Just copy what the open source browsers are doing already. For example:

AccessibilityTable::isDataTable()
http://trac.webkit.org/browser/trunk/Source/WebCore/accessibility/AccessibilityTable.cpp#L93


On Feb 21, 2014, at 2:19 AM, Leif Halvard Silli <xn--mlform-iua@xn--mlform-iua.no> wrote:

> After filing bug 24679 [1], which suggests to add more features to the 
> list of ”possible indicators”[2] for layout tables vs non-layout 
> tables, I was asked to provide data for the proposals. But how should 
> one go about providing data?
> 
> Web data is of what ultimately matters. But when identifying possible 
> indicators, it seems that knowing what features AT actually use for 
> discerning between layout and non-layout tables, would give us a good 
> shortlist of candidate indicators. Secondly, if we can spot some trends 
> in the (hopefully correct) data we already have, then that - as well - 
> could help us identify candidates. 
> 
> Today, its appears possible to glean following trends in the spec:
> 
> 1) Conformance, completeness amd semantics indicate non-layout
>   usage. The spec lists borders via CSS or @border=1, <th>,  
>   <thead>, <caption>, @headers, @scope.
> 2) Non-conforming ways to disable borders (border=0/cellspacing=0
>   cellpadding=0) plus role=presentation indicate layout usage.
> 3) @summary is ”not a good indicator” (this is probably based
>   *both* on Web data *and* AT behavior analysis
> 
>   Trends & AT data applied to: table@border
> 
> To me, HTML5’s table over “possible indicators” of (non-)layout usage, 
> seems correct, but not complete. However, in bug 24678,[3] Steve asks 
> for data about *one* non-layout indicator, namely border=1. But which 
> data? Web data? Assistive technology data? The fact that VoiceOver + 
> Safari matches spec w.r.t. borders as non-layout indication, ought to 
> put it on the shortlist of non-layout features. In another, somewhat 
> related, bug, Steve indicated that web data did not support that 
> table@border=1 indicates data tables.[4] My own toe dipping into same 
> pool told me the opposite.
> 
>   Trends & AT data applied to: <colgroup> with <col/> children.
> 
> It seems in line with the conformance & completeness trend that 
> VoiceOver+Safari treats <colgroup> with <col/> children[*] as indicator 
> of non-layout usage. What do other ATs do? What does Web data say? 
> Should the spec change accordingly? (PS: I know one HTML generator 
> which, for layout tables in XHTML1/HTML4, uses cellpadding=0 
> cellspacing=0, but which for HTML5 removes cellpadding/cellspacing and 
> *adds* <colgroup> with children, with bad results in VoiceOver as 
> result.)
> 
>   Trends & AT data applied to: lack of cellpadding=0 cellspacing=0[*]
> 
> Is it risky to delete cellpadding=0 cellspacing=0 from a table? 
> Could it cause an AT to treat a layout table, as a non-layout table? 
> This question seems relevant since authors are probably simply deleting 
> these attributes without adding @role=presentation in their place.
> 
>   Trends & AT data applied to: presence of sortable attribute
> 
> This is good candidate based on its strong link to data tables - it is 
> a semantic feature. But is is also possible to take the view that we 
> need implementation and usage before putting into the spec.
> 
> Finally: How important are heuristics for identifying data tables? Does 
> the situation remind about how UAs detect quirks vs no-quirks? (Except 
> in XHTML and @srcdocs (other exceptions?), no-quirks is triggered when 
> UAs detect a DOCTYPE that meets certain conformance and completeness 
> criteria.)
> 
> [1] https://www.w3.org/Bugs/Public/show_bug.cgi?id=24679
> [2] 
> http://www.w3.org/html/wg/drafts/html/master/tabular-data.html#the-table-element
> [3] https://www.w3.org/Bugs/Public/show_bug.cgi?id=24678
> [4] https://www.w3.org/Bugs/Public/show_bug.cgi?id=24647#c7
> [*] I did not check omitting <col/> child or omitting parent <colgroup>
> -- 
> leif halvard silli
Received on Friday, 21 February 2014 18:30:44 UTC

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