It's a subset of Javascript. HN discussion here https://news.ycombinator.com/item?id=32794081

This description reminds me of program language wars excerpt I saw somewhere years ago about how c was obviously superior to Pascal, because with enough preprocessor macros you can compile any Pascal program in c. Followed by some hideous and humorous examples.

This is amazing, an old school but effective approach in this modern age. I was afraid they were going to embed a browser.