Math conversion is handled by the texmath library. This is
specialized to math, and in the particular case you're interested
converts tex math to the math format used by Word.

Since it's specialized to math, it doesn't know how to handle
arbitrary non-math text of the sort that can go into an mbox.

There's not a good solution without changes in texmath's
architecture (one can imagine changing it so you pass in a parser
for normal text in the target format, which would be used inside
mboxes).

I wouldn't hold your breath, but you could put up an issue
on jgm/texmath on GitHub so we don't lose track.

M A writes:

> I'm converting from LaTeX to MS Word (.docx). LaTeX lets you embed the
> command
>
> \mbox{...}
>
> in LaTeX math mode. What goes inside the mbox is normal, non-math-mode
> text and commands. In my case, I have some special terms that I use
> outside of mathmode, which are italicized, e.g. like
>
> \textit{foo}
>
> I need to embed exactly the same text, formatted in the same way, in math
> mode. For example, in LaTeX, this is fine:
>
> $2 \times \mbox{\textit{foo}}$
>
> However, when using pandoc to convert to Word, I get this error:
>
> [WARNING] Could not convert TeX math '2\times\mbox{\textit{foo}}',
> rendering as TeX:
> 2\times\mbox{\textit{foo}}
> ^
> unexpected "\\"
> expecting "}", text, "{", "$", "$$", "\\(" or "\\["
>
> It appears that \mbox is not treated as an escape out to normal non-math
> mode, so that things that you could normally do in LaTeX in math mode are
> not understood by pandoc.
>
> Is this correct? Is this just an unimplemented feature? I know that
> pandoc can 't do everything that LaTeX does; that's OK. Is there a
> workaround?
>
> Thanks
>
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