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Re: img@relaxed CP [was: CfC: Close ISSUE-206: meta-generator by Amicable Resolution]

From: Benjamin Hawkes-Lewis <bhawkeslewis@googlemail.com>
Date: Sun, 5 Aug 2012 18:54:27 +0100
Message-ID: <CAEhSh3eOtdJz1QxBTsdqeE0O69Zpz4pkMk9DPf3j07=UU8YtSA@mail.gmail.com>
To: Leonard Rosenthol <lrosenth@adobe.com>
Cc: Sam Ruby <rubys@intertwingly.net>, "public-html@w3.org" <public-html@w3.org>
On Sun, Aug 5, 2012 at 5:21 PM, Leonard Rosenthol <lrosenth@adobe.com> wrote:
> PDF/UA (ISO 14289-1), however, has requirements throughout the document for the presence of Alt on Text, Images, Graphics, Annotations and even Math figures.  However, there is no requirement on the value of the Alt - so that an empty string could be valid according to the standard.  So a PDF/UA machine validator would flag missing Alt, but not an empty one. There were various reasons why that was a conscious decision by the committee.   One of the key reasons was around machine vs. human validation of accessibility considerations.  Validation of the value of an Alt can simply not be done by a machine - at least not today - and so a human has to be involved.  Since a human has to be involved anyway, there was no reason to put additional requirements on the machine.  This is true for a number of aspects of the PDF/UA standard - that we expected that the standard could NOT POSSIBLY be validated entirely by machine and would require (secondary) human validation.

Do you mean that there are two profiles of conformance for PDF/UA, a
full set of rules to be validated by humans (perhaps with machine
assistance) in which the value of Alt is checked (however
subjectively) and a second profile that formally subsets those rules
for machine-only checking? Or do you mean that PDF/UA only has one
(machine-checkable) set of rules, and that an Alt attribute that does
not conform to common sense (e.g. a photo of an apple described as a
photo of a house) would nevertheless be fully conforming to the
standard?

HTML and WCAG alike currently have some conformance requirements that
are not machine-checkable and other requirements that are, but they
don't formally designate which is which.

--
Benjamin Hawkes-Lewis
Received on Sunday, 5 August 2012 17:55:15 UTC

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