In the content section (in the panel) this would be used like this:
(accordion: open title: My accordion title )
Lorem **fat impsum** dolor…
(accordion: close)
the problem is that Lorem **fat impsum** dolor… will not be outputted as HTML but as plaintext (including the asterisks). I think this is due to the opening HTML tags <section> and <div> – because closing them in (accordion: open…) solves the problem (but of course makes no sense).
That’s a general problem with Markdown. HTML block tags prevent parsing of Markdown inside them.
For more complex tags like yours, it makes sense to implement a pre-filter instead. See the columns plugin for an example. It matches a set of two column tags (one opening and one closing one) and replaces them with custom HTML and the HTML representation of the Kirbytext inside the tags.
For bigger projects I guess the plugin would be the more performant solution. But in my case I will go for markdown.extra – which is such a no-brainer!