People keep asking me to add a Quick Look preview to Marked. I didn't want to embed one in the app because it's such a simplified version of Marked that I never saw the point. But to meet demand, I've submitted Marked QL to the App Store. Uses Apex (so it renders all flavors) and has all of Marked's themes (plus option to use custom style), MathJax, Highlight.js, Mermaid, etc. It's a good stopgap if you don't need all of Marked's flexibility but want some of its power at your fingertips/space bar.