mark extension doesn't seem to work

[iandall]

I'm using pandoc 3.1.3.

 $ echo '== foo ==' | pandoc -f markdown+mark
<p>== foo ==</p>

Is this expected?

[wlupton]

Omit the leading and trailing spaces?

% echo '==foo==' | pandoc-3.1.3 -f markdown+mark
<p><mark>foo</mark></p>