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Subject: AW: [docbook-apps] tagged and accessible PDF document with DocBook

Hi Holger,

we are generating PDF/UA from DocBook at work (but we use a different FO processor). 

The FO processors have support/extensions for
- role tagging to generate the tag structure (we handle this in the xsl layer, but of course autotagging may also be an option, if supported by the processor)
- document title as metadata title (dc:title)
- alternative texts for images
- actual text (e.g. for links)
- expansion text for abbreviations
Language information is also critical for accessible documents.

If you are interested, I can provide more information on how we modified the stylesheets.


-----Ursprüngliche Nachricht-----
Von: Holger Bast [mailto:holgerbast@gmx.de] 
Gesendet: Montag, 3. April 2017 22:12
An: docbook-apps@lists.oasis-open.org
Betreff: Re: [docbook-apps] tagged and accessible PDF document with DocBook

Hi there,
thanks all for your replies! Accessibility is getting more and more important, not only for public authorities.
I read a bit in the documentation of XEP http://www.renderx.com/files/XEPUserGuide.pdf as well as the link Tony provided. It seams to me that both processors already include their own interpretation mechanism for xsl:fo to apply a reasonable tagging structure.

If there is no specification in xsl:fo how to apply the right structural information there will be no normative instance and all processors will handle these kind of information in their own manner. I think the "role" attribute can be that kind of normative element that is suitable for this purpose. Nice would be some kind of switch (via parameter) that enables accessibility support for the fo-transformation. But I just started understanding the docbook-xsl files...

Here are some of my resources, maybe they can help you:

The following document gives a short overview how xml structural information can be applied to pdf. The document contains also a list of elements that should be tagged (see table 1) https://pdfs.semanticscholar.org/9a51/cd67046a81d4e02d6b4b35fa402bacc892f8.pdf

PAC 2 - PDF Accessibility Checker (PAC 2) PAC is an easy to use tool to check if your pdf document is accessible. If not PAC will show you the problems in the structure as well as inside the document.

And last but not least the pdf specification document. I didn't read the document yet. I try to get my hands on it in the next days.
ISO 14289-1:2014 - Document management applications -- Electronic document file format enhancement for accessibility -- Part 1: Use of ISO 32000-1 (PDF/UA-1) https://www.iso.org/standard/64599.html


Bob Stayton wrote:
> Hi Tony,
> Thanks for chiming in.  I guess I cannot expect to get an XSL-FO 
> standard for PDF tagging.  If we are going to implement it, we will 
> need to use the facilities in each XSL-FO processor.  Given that, I want to make sure what is output is usable, that is, meets the needs and standards of the accessibility community.
> I just ran across a webpage titled:
> http://508compliantdocumentconversion.com/finally-u-s-access-board-upd
> ates-interpretation-of-section-508/
> which says that WCAG 2.0 has been designated as the Reference Standard of section 508 of the Rehabilitation Act.
> I get that WCAG 2.0 is a W3C standard, but I don't know much about it. 
> Do you think I should spend time studying this as the correct reference for implementing standard and usable tags in DocBook XSL?
> Bob Stayton
> Sagehill Enterprises
> bobs@sagehill.net
> On 4/3/2017 11:52 AM, Tony Graham wrote:
>> On 03/04/2017 18:07, Bob Stayton wrote:
>>> Hi Holger,
>>> No, you didn't miss anything.  The DocBook XSL stylesheets currently 
>>> do not provide support for tagged PDFs.
>>> That said, my short investigation shows that implementing such 
>>> support is nontrivial.  Keep in mind that the DocBook stylesheets 
>>> don't actually create a PDF.  The stylesheets generate a FO version 
>>> of the document, and then an XSL-FO processor converts that to a 
>>> PDF.  So DocBook XSL has to generate additional markup in the FO 
>>> output that an XSL-FO processor can convert to PDF tags.
>>> It looks like each of the XSL-FO processors commonly used with 
>>> DocBook (FOP, XEP, and Antenna House) have different extensions for 
>>> implementing the FO needed to generate the PDF accessibility tags.  For example:
>>> FOP has fox:alt-text
>>> XEP has rx:pdf-structure-tag
>>> AH expects axf:pdftag
>> Not quite. If you produce either Tagged PDF or PDF/UA using AH 
>> Formatter from either XSL-FO or HTML/XML+CSS, then AH Formatter will 
>> default to generating a PDF Tag based on the type of the current 
>> element. For example, fo:root generates 'Document' and fo:table generates 'Table'.
>> See https://www.antennahouse.com/product/ahf64/ahf-pdf.html#taggedpdf
>> @axf:pdftag is for when you want to override a default mapping. See 
>> https://www.antennahouse.com/product/ahf64/ahf-ext.html#axf.pdftag. 
>> You can use @axf:pdftag to set a different standard PDF Tag for that 
>> element or you can provide your own non-standard Tag name, in which 
>> case AH Formatter will also generate the mapping from the 
>> non-standard name to the default PDF Tag for that element so that the 
>> requirement of the spec for Tagged PDF for having a mapping to a known Tag is met.
>>> This situation is similar to when PDF bookmarks were first implemented.
>>> Each XSL-FO processor had their own extensions to implement that 
>>> feature, and DocBook XSL had to support all three extensions.  When 
>>> XSL
>>> 1.1 standardized the markup for bookmarks, then all the XSL-FO 
>>> processors eventually implemented that standard and so did DocBook XSL.
>> ...
>>> I would be interested in adding PDF tagging to DocBook XSL.  It 
>>> would help if there were a clear spec for how to do so.  If I have 
>>> to figure it out for each of three XSL-FO processors, that's going 
>>> to take some time.
>> There is no current W3C Working Group for XSL-FO. There is the Print 
>> and Page Layout Community Group (https://www.w3.org/community/ppl/), 
>> of which I am the Chair, but it takes more than just a venue to 
>> produce a spec with enough impetus to convince multiple vendors/teams 
>> to implement it.
>> Regards,
>> Tony Graham.
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