Custom Elements are the lynchpin in the Web Components specifications. They give developers the ability to define their own HTML elements. When coupled with Shadow DOM, Custom Elements should be able to work in any application. But things don't always work seamlessly.
This project runs a suite of tests against each framework to identify interoperability issues, and highlight potential fixes already implemented in other frameworks. If frameworks agree on how they will communicate with Custom Elements, it makes developers' jobs easier; they can author their elements to meet these expectations.
Custom Elements and Shadow DOM don't come with a pre-defined set of best practices. The tests in this project are a best guess as to how things should work, but they're by no means final. This project is also about driving discussion and finding consensus, so don't be afraid to open a GitHub issue to discuss places where the tests could be improved. ✌️