Rule: Headers attribute only refers to cells in the same table (a25f45)

[jeeyyy]

Rule: headers attribute only refers to cells in the same table

Closes issue: #406

Note:
For clear intents and purposes, the scope of this rule is kept to be fairly simple.
Intent is to author more rules for various other scenarios that involves this SC.

Updated

[carlosapaduarte]

Some minor requests for change.

[ShadowBB]

Apart from the comment Wilco left about included in the accessibility tree I approve this rule.

Updated

[WilcoFiers]

Every screen reader we've tested this in will look at row/column headers for fallback. That may not be what the algorithm says they should do, but someone testing with one of the top 4 AT / browser combinations is not going to see a problem here. I find this test case questionable. Here's the test case we ran a little while ago:

<table>
  <tr>
    <th scope="col">Projects</th>
    <th scope="col">Progress</th>
  </tr>
  <tr>
    <td headers="projects100">My Project</td>
    <td>15%</td>
  </tr>
</table>

IE + JAWS: Works
Chrome + JAWS: Works
Firefox + NVDA: Works
Safari + VO: Works

[Jym77]

If this passes the SC (which I don't challenge), then the rule need to be changed to take fallback headers into account.
This certainly fails the rule right now, so if this passes the SC, the rule is bad.

And the rule in its current version is not referencing the assignation algorithm anymore…

(technically, the rule does assume that there is no fallback headers, but if this assumption is false for the vaste majority of cases, it needs to go away)

Updated

[jeeyyy]

Given the changes to the examples, I am adding another 1 week to this PR for final call, which will end on 24th Feb 2020