Bottom line: we can't expand org-html-mathjax-options to add in MathJax's
cancel.js, etc. Yes, your first "quick-and-dirty" worked just fine. Q: How
did you know how to format #+html: \(\require{cancel}\) ? Also, how does
the org world know that we're talking about loading MathJax's cancel.js? As
you all know I'm not a "developer-class" poster here, so my questions often
look dull-witted. Will try the patch once I learn a bit more diff in Emacs
lore. . . .

On Thu, Nov 2, 2017 at 9:12 AM, Rasmus <rasmus@gmx.us> wrote:

> Lawrence Bottorff <borgauf@gmail.com> writes:
>
> > I'm trying to get a typical Latex strikethrough with MathJax in an HTML
> > export, i.e., \cancel{thing} puts line through "thing". This
> > <http://docs.mathjax.org/en/latest/tex.html#cancel> tells me how. But I
> > don't know how to include this MathJax markup in an org file for HTML
> > export. If I forego MathJax -- i.e., #+OPTIONS: tex:dvipng instead
> > of #+OPTIONS: tex:t -- \cancel works, but I need to use MathJax. It
> doesn't
> > look like orhg-html-mathjax-options is expandable. . . .
>
> For now this works for me:
>
>     #+html: \(\require{cancel}\)
>     \begin{equation}
>     \cancel{x = 1}
>     \end{equation}
>
> Cf. http://docs.mathjax.org/en/latest/tex.html#tex-and-latex-extensions
> You could also autoload the extension, cf. https://github.com/mathjax/
> MathJax/blob/master/test/sample-autoload.html
>
>
> That being said, I don’t think extensions were available at the time
> #+HTML_MATHJAX was introduced.  We could add extension support, but the
> questions would be whether to add them to #+HTML_MATHJAX or make a new
> keyword, e.g.
>
>     #+HTML_MATHJAX_EXTENSIONS: ext1 ext2 ... extN
>
> I guess it would default to the "autoload-all" extension.
>
> One issue is that some of them have configuration options, like "noError".
>
> If you want, you can try the attached patch.
>
> Rasmus
>
> --
> Vote for proprietary math!
>