Question: how to handle "fill in the blanks"?

[TimArborealis]

How do we suggest handling fill in the blanks-type of content inside math expressions? Example:

Is <menclose class="MathML-Blank"> viable?

[samimaattaCelia]

Menclose

This is what I got when trying <menclose notation="box"> on Firefox:

On Chrome:

Chrome + MathJax:

MathCAT says "empty box" for every box in the matrix, which also works even if it's a bit verbose.

Anonymous <mrow> boxes

From MathML Core I would lean on just using an <mrow> as an anonymous box. It can be used to handle layout. It would also work nicely with MathCAT, because it says "empty" on every cell of the matrix that is empty.

The problem was that I couldn't get it visually the same with the boxes. Maybe there would be a CSS trick to do that, but I don't know how much we should rely on that, because reading software can anyways just omit the styles if the theme changes.