I'm working through the tutorial on the WSIWYG official webapp now. The syntax for equations is remarkably intuitive! I tried a few things from guessing after skimming the tutorial, and they mostly worked in the most intuitive way. Here is what I gather this is. A mix of:

  - Markdown general formatting (images, lists etc)
  - LaTeX or MathJax-like equation syntax
  - A rendering engine and software that turns these into pixels