@epa-wg/custom-element is a devtools helper for the Declarative Custom Element implementation. It provides a "Transformation" tab in the DOM inspector, allowing developers to explore the data and template used for rendering HTML. Developed by Sasha Firsov, this Chrome add-on is a valuable tool for debugging and understanding the inner workings of the Declarative Custom Element.

Using HTML template and XSLT syntax, @epa-wg/custom-element transforms data into HTML. The "Transformation" tab in the DOM inspector provides a transparent view into the data and template, making it easier for developers to analyze and debug the rendering process. This feature is particularly useful when debugging complex templates and identifying issues in the transformation process.

Additionally, the plugin allows developers to copy both the data and template into files, enabling step-by-step debugging in an IDE. This feature further enhances the debugging capabilities of @epa-wg/custom-element, providing developers with a comprehensive toolset for working with Declarative Custom Elements.

Overall, @epa-wg/custom-element is a valuable devtools helper for developers working with Declarative Custom Elements. Its "Transformation" tab and file copying features make it easier to explore, debug, and understand the rendering process, enhancing the development workflow.