PDFlib 8 Windows COM/.NET Tutorial

With this ordering of structure elements the main text (which spans one and a half columns)
is interrupted twice for the table and the insert. Therefore it must also be activated
twice using activate_item( ).
The same technique can be applied if the content spans multiple pages. For example,
the header or other inserts could be created first, and then the main page content element
is activated again.
10.5.4 Using Tagged PDF in Acrobat
This section mentions observations which we made while testing Tagged PDF output in
Adobe Acrobat 8/9/X. The observations below are mostly related to bugs or inconsistent
behavior in Acrobat. Unless mentioned otherwise the observations relate to Acrobat 8 ,
9, and X. A workaround is provided in cases where we found one.
Acrobat’s Reflow Feature. Acrobat allows Tagged PDF documents to reflow, i.e. to adjust
the page contents to the current window size. While testing Tagged PDF we made
several observations regarding the reflow feature in Acrobat:
> The order of content on the page should follow the desired reflow order.
> Symbol (non-Unicode fonts) can cause Reflow in Acrobat 8 to crash, and can disable
Reflow in Acrobat 9. For this reason it is recommended to put the text in a Figure element.
This problem is fixed in Acrobat X.
> BLSEs may contain both structure children and direct content elements. In order for
the Reflow feature (as well as Accessibility checker and Read Aloud) to work, it is recommended
to put the direct elements before the first child elements.
Structure items with mixed types of children (i.e., both page content sequences and
non-inline structure elements) should be avoided since otherwise Reflow may fail.
> The BBox option should be provided for tables and illustrations. The BBox should be
exact; however, for tables only the lower left corner has to be set exactly. As an alternative
to supplying a BBox entry, graphics could also be created within a BLSE tag,
such as P, H, etc. However, vector graphics will not be displayed when Reflow is active.
If the client does not provide the BBox option (and relies on automatic BBox generation
instead) all table graphics, such as cell borders, should be drawn outside the
table element.
> Table elements should only contain table-related elements (TR, TD, TH, THead, TBody,
etc.) as child elements, but not any others. For example, using a Caption element
within a table could result in reflow problems, although it would be correct Tagged
PDF.
> Acrobat 8 and 9: Content covered by the Private tag will not be exported to other formats.
However, they are subject to Reflow and Read Aloud, and illustrations within
the Private tag must therefore have alternate text.
> Reflow seems to have problems with PDF documents generated with the topdown
option.
> If an activated item contains only content, but no structure children, Reflow may
fail, especially if the item is activated on another page. This problem can be avoided
by wrapping the activated item with a non-inline Span tag.
> Acrobat cannot reflow pages with form fields (including digital signature fields), and
will display a warning in this case.
> Acrobat 8: every reflow problem disables the Reflow feature and disables its menu
item.
274 Chapter 10: PDF Versions and Standards (Edition for COM, .NET, and REALbasic)