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Proposed: a TN tag to join TH and TD?

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From: Duff Johnson
Date: Jun 10, 2013 9:23PM

Some of us who are thinking about PDF 2.0 are thinking about tables.

Specifically, we note that many tables include cells that are (usually) empty, but also serve no real purpose in the table except to keep the rectangular arrangement of cells intact.

Yes, simpler tables are best for accessibility purposes, but like them or not, complex tables are pretty unavoidable. "Dead" cells happen in tables; it's a fact of life, but what's the right way to recognize this fact? I know that in practice there are lots of empty TH and TD cells out there - but that's not necessarily ideal.

In the current PDF 1.7, there's no consistent markup for this use case.

One solution we are thinking about is a new cell type to join TH and TD. We're thinking it's called TN, for "no-op".

The most common use of TN would be at the empty "corner" of a table (a very common case) or (less commonly) in the middle of a TH row or column, or where one might otherwise expect a <TD> cells filling a gap. TN differs from an empty TD because TN, by definition, never contains anything of significance.

TN cells have no table function except to fill gaps between other cells. An AT processor wouldn't be expected to report on or inquire within a TN tag. If queried, the cell would report as "intentionally unused" or equivalent.

(There is some question as to whether the use of TN cells in TH rows or columns may create ambiguity in the table structure, and force the use of explicitly linked headers).

A TN cell should not contain semantically relevant content. Options that are OK are:

- visual indicators that the TN ios not just an empty TD cell but rather a no-op cell
- text amounting to "intentionally unused"
- similar stuff

My questionÂ… what's the "right" way to handle such cells from the HTML point of view? How has the discussion on this question (if any) proceeded in the world of HTML accessibility? What's the right solution, from your point of view, for this common case?

Or perhaps it doesn't matter - maybe empty TH and TD cells don't cause any real problems?

Thanks,

Duff Johnson

Independent Consultant
ISO 32000 Intl. Project Co-Leader, US Chairman
ISO 14289 US Chairman
AIIM Standards Board Chairman & member, AIIM Board of Directors
PDF Association Vice-Chairman

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