The Jade object has 3 panes. The first one is the ACE Jade Editor. It does Jade syntax checking, and flags you if you make a mistake. The second one is the generated javascirpt. The third one is the generated html. When the user clicks the save button, the HTML is generated, and uploaded to the server along with the original jade content.
Native Jade makes multilingual websites easy. A Jade Language Editor would allow a translator to translate only the text in his language in a Jade template.
Here is an excellent way to learn Jade. Just edit the jade, and watch the generated html appear in the other window.