The good thing is it's very easy to design the web portion in JS sketchbooks such as jsbin/codepen/jsfiddle because the snippet code structure maps cleanly to this. The bad part is that WKWebView doesn't always behave consistently or have a clean slate. Maybe this will help resolve state issues in the future. It will randomly not be able to find injected scripts without any code changes, and I haven't figured out why.
In this, a two-column table in HTML can be filled with values from Lua tables, and can also send them back. This is used for HTTP requests with arbitrary headers in a fun and exciting way.