Live coding on Reveal.js

I'm interested in creating a presentation using Reveal.js

I really like to know that what techniques or plugins did the speaker use to make his presentation editable e.g. in YouTube Clip where he edited some HTML coding on a page then he got the updated version of Angular App on another page

I've tried to read the Reveal.js's documentation and searched on google but I cannot find anything related

Please guide me what to do

Thanks