You can use /sandbox/ for writing and testing your own code. Nothing in /sandbox/ will get checked into the repo, except files that end in .example (so don't edit or add those files). To get started make a copy of index.html.example and rename it to index.html.

npm start will automatically copy these files over from .example if they don't already exist.

open http://localhost:9999/sandbox/noUITitleAttributes.html