This demo web app is nothing but static HTML and JavaScript files. However, since it uses Ajax, you have to host it on a web server to make it work.
Live demo at http://stevesanderson.github.io/ko-custom-elems-test/
Running it locally
If you have Node.js, open a terminal/command prompt in the same directory as this README file, then run:
npm install -g http-server
http-server
... then browse to http://localhost:8080/
Alternatively, configure any other web server to serve these files.