It may be similar to Markdown if you squint your eyes real hard, but it's not Markdown. Furthermore, quoting a random snippet without any elaboration is unhelp

It may be similar to Markdown if you squint your eyes real hard, but it's not Markdown. Furthermore, quoting a random snippet without any elaboration is unhelpful and only serves to confuse people (as it already did for the other comment!) # means "evaluate". figure(...) is the function being evaluated. The syntax inside figure(...) is fairly regular, not too different from what you'd see in typical programming languages (but with a document-oriented twist like the %). <figure> may seem to be related syntatically to #figure(...), but it's not. It's just a label. Like an HTML div tag with id="figure". It can very well be changed to <foo> in your example and it'd still work.