The viewer is open source[0], so yeah you can embed it in an iframe (that's what the editor does), and just `postMessage` the parsed markwhen and some additional state to it. The structure of the posted data is here[1]. I'm happy to help, rob@markwhen.com or I'm in the markwhen discord[2]
Would my app be able to generate a Markwhen file and then embed the viewer to view it? Would that be free or paid?