\dot breaks \color ?

[dginev]

One of our Authorea users brought to our attention that his "blue dotted W" macro wasn't rendering successfully in MathJax, so I am propagating the request here.

Minimal example:

Broken: ${\color{blue}\dot{W}}$
Renders great: $\dot{{\color{blue} W}}$

I am guessing the expected MathML for the broken example is something on the lines of:

    <mover accent="true">
      <mi mathcolor="#0000FF">W</mi>
      <mo mathcolor="#0000FF">&#x2D9;</mo>
    </mover>

Thanks for the support!

[dpvc]

The default color macro in MathJax takes two arguments, the color and the math to be colored. This is in contrast to the LaTeX implementation, where \color is a switch that changes the active color. So {\color{blue}\dot{W}} will act like \color{blue}{\dot} W, which is invalid, since it will try to processes \dot without any argument. So you would need \color{blue}{\dot W} instead.

If you want the LaTeX-style color command, you must load the color extension via

  TeX: {extensions: ["color.js"]}

in your MathJax configuration, or via \require{color} within an expression on the page.

[dginev]

Thanks for the explanation and the recipe on getting the TeX behaviour! It works like a charm.

It was a bit of a gotcha for us, since we weren't aware MathJax has decided to reinterpret some of the standard LaTeX macros. Is there a list of other known differences, so that we can prepare for similar situations with other commands?

Thanks again, I am closing here.

[dpvc]

There are very few (intentional) differences. The \color macro is the major one, plus some relaxed syntax for \llap, \rlap, \raise, and \lower. See #133, #1694, and #29 for some discussions of these issues.