Earlier this summer, Riley Napier from our engineering team joined me for our June 24th Courier Live to help me build a Slack Slash Command to display estimated departure times for BART Stations. We created a Glitch ExpressJS app to accept the commands and Courier to handle the responses. We designed the messages by dynamically generating Block Kit using Jsonnet.
Shadow DOM is an API for DOM encapsulation. It's perfect for when you need to embed a widget in a DOM you don't have access to.