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Re: Untagged PDF doc with table structure

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From: Chagnon | PubCom
Date: Feb 18, 2015 11:17AM

Lynn wrote: " in PDF docs, what's the difference between tags and structure?
"

This is one of the toughest concepts we teachers have to explain! I'd love
to hear how others describe it. Here's my take:

Tags are labels. Code labels, specifically, that are read by Assistive
Technologies and are not usually visible to sighted users unless they have
Acrobat Pro. They let AT users know what's a heading 2, a list of bullets,
tables, and other parts of the documents. Tags also do a lot of work for us,
such as assisting us in creating bookmarks and tables of contents, creating
navigation systems, and holding the Alt-text on graphics (Alt-Text is an
attribute on the figure tag and doesn't stand alone on its own).

Structure is the sequence of how the document's pieces will be read, or in
other words, the sequence in which the tagged items are read. Call it
reading order or tag reading order. The structure of some documents can also
have nesting qualities, such as all the pieces of a chapter, and all the
chapters in a book.

An example: If Heading 1 designates a chapter title, then all the paragraph,
bullets, tables, and heading 2 items within that chapter will be nested
inside the main heading 1 tag. This allows AT software to figure out,
hopefully, what goes with what; that all the tags nested within Heading 1 is
a chapter.

Structure is created when you have tags (the right tag labels) and a reading
order (a logical reading order). It is possible that a tagged and structured
document might not be fully accessible because the tags aren't accurate
enough or the reading order is out of whack.

Example number 1: In older versions of MS Word, figures would be placed in
very odd places of the reading order when it was exported to a PDF. If
paragraph 1 stated "see figure 5", figure 5 itself might end up at the very
end of the reading order, not near paragraph 1 where it was referenced. A
sighted person sees figure 5 next to the paragraph, but a screen reader user
doesn't hear it voiced until the last page, and maybe that's page 360 of a
long government document. So the document is tagged and structured, but it's
a faulty structure because the reading order is incorrect.

Example number 2: Graphic designers who use desktop publishing programs like
Adobe InDesign and QuarkXpress create very complex visual layouts. Visually,
things aren't designed in a traditional top down left right pattern but
instead could be scattered all over the physical page. Here's an example of
a 2-page magazine spread:
http://fc02.deviantart.net/fs71/i/2010/082/e/c/Magazine_Layout_Design_1_by_B
reakTheRecords.jpg (This is just a random sample I pulled up on the
Internet, so it is only a graphic of a 2-page spread, no live text or
Alt-text.)

Note that article title (or heading 1) appears on page 2, and the body text
of the story starts on page 1. Backwards! And then there are 2 quotes at the
top of page 1, so obviously the designer wants us to read those at the
beginning of the story, also. And here's a similar example:
https://m1.behance.net/rendition/modules/12455236/disp/322ee0c042b2949607393
d8b1f24ad96.jpg

Whew! Getting a tagged, logical reading order from this type of publication
isn't easy!

Summary:
Structure equals tagged content placed in a logical reading order.

Well, that's my attempt. Would love to hear how others describe the
concepts.

--Bevi Chagnon