problem with rules in mathjax array about instiki HOT 2 OPEN

This isn't really a MathJax issue, it's an itex issue.

In MathML, the functionality you want is controlled by the columnlines and rowlines attributes on the mtable element. Thus the following MathML output produces the table you want:

<math class='maruku-mathml' display='block' xmlns='http://www.w3.org/1998/Math/MathML'>
<mtable columnalign='right right right right right' columnlines='solid none none none' rowlines='solid none none none' displaystyle='false' rowspacing='0.5ex'>
 <mtr><mtd>*</mtd> <mtd><mi>A</mi></mtd> <mtd><mi>B</mi></mtd> <mtd><mi>C</mi></mtd> <mtd><mi>D</mi></mtd></mtr>
 <mtr><mtd><mi>A</mi></mtd> <mtd><mi>A</mi></mtd> <mtd><mi>B</mi></mtd> <mtd><mi>C</mi></mtd> <mtd><mi>D</mi></mtd></mtr>
 <mtr><mtd><mi>B</mi></mtd> <mtd><mi>B</mi></mtd> <mtd><mn>2</mn><mi>B</mi></mtd> <mtd><mi>D</mi></mtd> <mtd><mn>2</mn><mi>D</mi></mtd></mtr>
 <mtr><mtd><mi>C</mi></mtd> <mtd><mi>C</mi></mtd> <mtd><mi>D</mi></mtd> <mtd><mi>C</mi><mo>+</mo><mi>D</mi></mtd> <mtd><mn>3</mn><mi>D</mi></mtd></mtr>
 <mtr><mtd><mi>D</mi></mtd> <mtd><mi>D</mi></mtd> <mtd><mn>2</mn><mi>D</mi></mtd> <mtd><mn>3</mn><mi>D</mi></mtd> <mtd><mn>6</mn><mi>D</mi></mtd></mtr>
</mtable>
</math>

Unfortunately, itex doesn't currently support the columnlines and rowlines attributes (neither using the "standard" LaTeX syntax you were using, nor via some alternative syntax).

This is an unfortunate omission, which I hope to rectify in the next version of itex2MML.

from instiki.

So I've been thinking some more about this, but I am a bit stymied. The semantics of columnlines, rowlines (and, as I'll explain, frame) are completely different from what's allowed in the LaTeX array environment.

• columnlines and rowlines control the lines between rows/columns. LaTeX allows you to put a vertical line before the first column or after the last one, merely by inserting a "|" (and similarly for an "hline" before the first row or after the last row). In MathML, the only option (controlled by the frame attribute) is whether to put a box around the entire array.
• In LaTeX, you can insert a double (or triple or whatever) line with a "||" (or "\hline\hline"). In MathML, the only options are "none", "solid" or "dashed".

Setting aside the intricacies of how to implement something like this, these incompatibilities are going to create serious headaches ...

from instiki.