[Webkit-unassigned] [Bug 20260] The conflict resolution algorithm for table borders in the collapsed borders model should only affect the segment of border that is actually shared between the two cells

Thu Oct 20 18:02:52 PDT 2011

https://bugs.webkit.org/show_bug.cgi?id=20260

Tab Atkins <tabatkins at google.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|border-collapse collapse    |The conflict resolution
                   |paints border on the wrong  |algorithm for table borders
                   |table cell                  |in the collapsed borders
                   |                            |model should only affect
                   |                            |the segment of border that
                   |                            |is actually shared between
                   |                            |the two cells
             Status|UNCONFIRMED                 |NEW
                 CC|                            |tabatkins at google.com
     Ever Confirmed|0                           |1

--- Comment #2 from Tab Atkins <tabatkins at google.com>  2011-10-20 18:02:52 PST ---
This behavior is undefined, but Firefox does better than us here, so I'm considering it a valid QoI bug.  A better reduced testcase is included at the end of this comment.

The problem is that, when we resolve border conflicts in the collapsed borders model, we don't treat col/rowspanning elements specially.  If a single-cell <td>'s border wins over a neighboring spanning <td>, the spanning <td> applies the new style across its entire border edge, rather than just the segment of its border that it shares with the single-cell <td>.

We should instead limit the effect to only applying to the segment of border that is actually shared between the two cells.

Reduced test case:
<!DOCTYPE html>
<table>
 <tr>
  <td class=border></td>
  <td></td>
 <tr>
  <td colspan=2></td>
</table>

<br>

<table style=border-collapse:collapse;>
 <tr>
  <td class=border></td>
  <td></td>
 <tr>
  <td colspan=2></td>
</table>

<style>
td { min-width: 20px; height: 20px; background: silver; border: thick solid black; }
.border { border-bottom-color: red; }
</style>

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