Excellent point. I had forgotten about this. I work for a non profit so I’m ok, but yes you should absolutely check the terms of the license before using. On the upside, almost everything is markdown files in regular folders, so you can fall back to vim anytime.
Yes this is a thing and it’s been around for quite some time. If you’re trying to approximate TeX, you may also be interested in MathML.
I need to go lay down; I’m having flashbacks to the good old days of “XML everywhere for everything all the time”.