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Re: We are where we are.... but how did we get here?

From: Lachlan Hunt <lachlan.hunt@lachy.id.au>
Date: Sat, 02 Jul 2005 16:19:53 +1000
Message-ID: <42C63209.9090405@lachy.id.au>
To: "L. David Baron" <dbaron@dbaron.org>
CC: www-style@w3.org

L. David Baron wrote:
> There are much simpler solutions for the problem of column styling than
> a second pass of selector matching.  For example, we could have column
> selectors that select based on the table semantics of the underlying
> content (rather than how that content happens to be displayed).

Yes, I fully agree with this idea which is much like what I previously 
wrote [1].  However, I've been thinking about the limitation of only 
being able to apply :nth-column to elements which are semantically 
tabular, as defined by the markup language, rather than any element the 
author wants treated as struturally/visually tabular.

I've been thinking what if there were a way to decleratively describe 
the structure of the markup (independant of how the document is finally 
displayed) in a way that lets the UA calculate the columns before layout 
is done, or, infact, even before the cascade.

Here are my first thoughts on how this could possibly be achieved.  It 
is by no means a formal proposal of any kind, just a bit of 
brainstorming to get the ball rolling.

We've already established that's it's not possible to achieve this based 
on the 'display' property, and therfore using "display: table-*;" as a 
way to determine an element is a table-cell, for example, for the 
purpose of calculating which column it fits in is not feasible.  So, 
what we need is a way to unconditionally declare that some element *is* 
a table, or *is* a table-cell, etc. regardless of how it is eventually 
rendered.

My first idea is to use an @-rule that contains such declarations.  For 
example: (I'll use the HTML table element names for simplicity, but the 
idea is that it could apply to any elements the author chooses)

@table {
   table: selector(table);
   table-row-group: selector(table tbody, table thead, table tfoot);
   table-row: selector(table tr);
   table-cell: selector(table tr td);
   table-cell-colspan: attr(colspan);
   table-cell-rowspan: attr(rowspan);
   ...
}

The idea is that the above declares which elements should be considered 
part of a table structure for the purpose of calculating which table 
structure related selectors, such as :nth-column() or :nth-row(), apply. 
  Note that this is completely independant of how such elements will be 
rendered, and doesn't not affect the default 'display' value of the 
selected elements in anyway.

Now that the the UA is able to determine the structure of table markup, 
and it can determine which elements are table cells and how determine 
how many rows or columns it spans structurally, it should be possible to 
calculate things such as which column a cell belongs to, structurally.

e.g.

<table>
   <tr>
     <td colspan="2">r1d1 r1d2</td>
     <td colspan="2">r1d3 r1d4</td>
   </tr>
   <tr>
     <td>r2d1</td>
     <td rowspan="2">r2d2 r3d2</td>
     <td>r2d3</td>
     <td>r2d4</td>
   </tr>
   <tr>
     <td>r3d1</td>
     <td>r3d3</td>
     <td>r3d4</td>
   </tr>
</table>

:nth-column/row could be defined to either select only the cells that 
start in the selected column/row or all cells the span the selected 
column/row.  Perhaps this could be another aspect declared in the @table 
rule.  For the purposes of this, I'll assume they only select the cells 
that start in the selected column/row.

td:nth-column(1) should select cells r1d1, r1d2 and r1d3
td:nth-column(2) should select cell r2d2
td:nth-column(3) should select cells r1d3, r2d3 and r3d3
td:nth-column(4) should select cells r2d4 and r3d4

They should select even if they're not rendered as table cells. i.e.
td:nth-column(2) { display: block; } does not cause any circular 
references, the selector still applies based on the structure of the 
document, which is declared in the above @-rule.

[1] http://www.w3.org/mid/42BFEB1B.2010203@lachy.id.au

-- 
Lachlan Hunt
http://lachy.id.au/
Received on Saturday, 2 July 2005 06:20:10 GMT

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