Fortunately I found what I needed in multimarkdown, based on markdown, though people have to install it from source at present.
Home: https://fletcherpenney.net/multimarkdown Download: https://github.com/fletcher/MultiMarkdown-6/releasesI'm writing to suggest including multimarkdown in Debian as I assume I'm not the only one who found it useful. It's (almost!) exactly what I needed with the only proviso that [[Link]]s have to be [Links](Links) to work in both contexts and, when using it to translate markdown to html, href="Link" needs to be href="Link.html" but those are both easily fixed with one-line sed scripts.
Thanks again and keep up the good work M
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