https://bugs.documentfoundation.org/show_bug.cgi?id=160196

--- Comment #11 from [email protected] ---
Hi Tomaz,
   Structure Destinations (SDs) are clause 12.3.2.3 of ISO 32000-2:2020 (no
cost edition). They look like standard Destinations but reference a structure
tree element rather than a page object. 

PDF/UA-2 is a licensed ISO publication so I cannot share or quote it as you
know, but if you look at the PDF Association's free "Well-Tagged PDF"
Specification (https://pdfa.org/wtpdf) and follow its guidance you will be 100%
compliant to PDF/UA-2 in all aspects. Helpfully, the WTPDF clauses use the same
numbers as PDF/UA-2 so just look at WTPDF clause 8.8 for SDs...

BTW I did find other issues with my testing of LibreOffice-Dev concerning the
combination of PDF/A-1 and PDF/UA-1. This is a very interesting combination as
PDF/A-1 was written against Adobe PDF 1.4 while PDF/UA-1 was written against
ISO 32000-1:2008 (PDF 1.7) - this means some PDF/UA requirements cannot be met
with a PDF 1.4 feature set (e.g. the Tabs entry; certain structure elements;
etc as they were all introduced from PDF 1.5 to PDF 1.7). PDF/A-2 and PDF/A-3
are both also written against ISO 32000-1:2008 so either of these will be OK. 

I'm seeking guidance and recommendations from our community of experts, but I
think(!!) our recommendation will be PDF/UA-1 is only compatible with PDF/A-2
or PDF/A-3 and not PDF/A-1 - and that such dual-conforming files should always
be marked as PDF 1.7 (unless you really want to write a lot of code to jump
thro' hoops and work out precise versioning - which I would strongly recommend
against). Technically PDF/A-1 is superseded by PDF/A-2 and PDF/A-3 and
equivalent capable - there is NO technical reason to PDF/A-1 anymore. 

When there is a formal answer available I will post back here but for now
please consider the above (i.e. don't allow PDF/A-1 and PDF/UA-1 combination -
or force it to PDF/A-2 or PDF/A-3 whenever PDF/UA-1 is used). Similarly
PDF/UA-1 cannot be used with PDF 2.0 files - that is what PDF/UA-2 is for.

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