```
% pandoc -f latex -t native
\newcommand\foo{+}
Testing: $\mu\foo\eta$.
^D
[ Para
[ Str "Testing:", Space, Math InlineMath "\\mu+\\eta", Str "." ]
]
<!-- It would be nice to handle this case, but I don't
know how:
\newcommand{\vecx}{a + b}
$\hat\vecx$
[Para [Math InlineMath "\\hat{a+b}"]]
-->