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Re: Proposed: a TN tag to join TH and TD?

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From: Jukka K. Korpela
Date: Jun 11, 2013 1:47AM

2013-06-11 6:23, Duff Johnson wrote:

> "Dead" cells
> happen in tables; it's a fact of life, but what's the right way to
> recognize this fact?

It depends on why they are dead.

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

The same applies to HTML.

> 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".

You would need to define the meaning differently, in more structural, or
"semantic" terms. Moreover, it's not clear that a new tag would be the
best approach, especially since we don't want old software to choke with
a document just because we have improved its tagging. In HTML at least,
I would strongly recommend proposing a new attribute rather than a new
element. This would let browsers keep doing what they are doing now,
just ignoring the attribute. In HTML5, it could be a "boolean" attribute
(a pure keyword attribute), e.g. <td dummy> or <th dummy>.

> 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.

The first case is clear and can easily be explained and defined. There
would be a cell in a table such that other cells in the same row are
column headers and other cells in the column are row headers, leaving no
choice for this cell to be anything but a filler, required to make the
table regular.

On the other hand, in HTML, such a situation could be recognized from
other markup if scope attributes are used for those other cells.

But what other cases would there be? I would propose starting with the
hypothesis that all other cases can be handled as normal cells with some
logical content that may physically be displayed and spoken as blank but
isn't really comparable to the dummy cells. On my page about empty cells
in HTML, I suggest various ways to make cells not empty in data content
even though they lack normal data:
http://www.cs.tut.fi/~jkorpela/html/emptycells.html

A common example is to use "N/A" or maybe a dash to indicate that some
data is not available or not applicable. Such cases are different from
the dummy cells, because it is about the data, not the table structure.

Consider a simple example where a table is a matrix that shows distances
between cities, with the same cities appearing as column headers and as
cell headers. Then the upper left corner is really a "dummy" cell. The
diagonal elements that indicate distance from a city to itself are
really "not applicable" and could be left blank (or, better, gray, or
with a dash as the content), but they are not dummy in the table
structure - rather, they indicate trivial data and could logically
contain 0. Similarly, the cells between the diagonal could be left
empty, since they contain redundant information (assuming metrics where
distance from A to B equals distance from B to A), but this too is a
feature of the data, not something that should be reflected in table markup.

So I would say that as a rule of thumb, when a table cell would be empty
due to lack of data or because data is not relevant, it should be marked
up as a normal cell, and we should consider whether some character data
should still appear in it. And really dummy cells are probably a special
case that can be handled with existing markup or that does not need any
particular handling.

Yucca