Illustration elements requirements around BBox differ in PDF 1.7 and PDF 2.0, but not discussed in ISO TS 32005

[petervwyatt]

In ISO 32000-1:2008 (PDF 1.7), the paragraph below Table 340 states "An illustration may have logical substructure, including other illustrations. For purposes of reflow, however, it shall be moved (and perhaps resized) as a unit, without examining its internal contents. To be useful for reflow, it shall have a BBox attribute. ..." where "it" means any of the PDF 1.7 illustration elements Figure, Formula or Form. Note the "shall" requirement for the BBox attribute. I also note that some PDF/UA-1 validators check for this while others do not.

ISO 32000-2:2020 (PDF 2.0), clauses 14.8.4.8.5 (Figure) and 14.8.4.8.6 (Formula) restate this as recommendations (3rd and 4th paragraphs respectively): "It should have a BBox attribute (see 14.8.5, "Standard structure attributes")." I cannot find any equivalent statement for Form and BBox so I assume this was weakened to just a permissive "may"...

This difference in PDF 1.7 "shall" vs PDF 2.0 "should" for illustration elements and BBox is not mentioned in ISO TS 32005 AFAICT, so seeking clarification for each of the reuse and accessibility use cases - especially if consensus is that BBox is not required for PDF/UA-1 (as per some (but not all!) validators).

[car222222]

But surely there are many other, similar, small changes between the provisions of 1.7 and 2.0: do they all need to be documented?

If there are a substantial number of similar changes, then a new document is
very likely needed for them.
But the only, or primary, purpose of 32005 is not at all related to the discussion
of such changes from 1.7, is it?

Going further!
The following more general suggestion for extra wordings probably needs a new issue:

It would probably be better to make it clear, possibly in 32005, that PDF2.0 (32000-2) is completely independent of earlier versions, and of 32000-1.
Thus nothing from 32000-1 needs to be known, understood, considered or obeyed when constructing a PDF 2.0 document.
This still applies even when using “PDF1.7 types in a PDF2.0 document”, when only the provisions in 32005 (and 32000-2) need to be known and followed.

This would clarify and reenforce the fact that 32005 is no more than an extension
of 32000-2 and that it is not related at all to any contents of, or provisions in, 32000-1.

[car222222]

Another related specific clarification is needed, somewhere.

None of the category assignments in 32000-1 (for SE types) remain effective in either 32000-2, or in its extension 32005.

This may need some explanation in 32005.