Dave Raggett's excellent HTML Tidy lived here at SourceForge! And this site is kept for historic reasons only. Bugs, issues, feature requests should be filed on the current github site.
This project worked nice in the past with Html 4 but it has a very severe design error: It internally maintains detailed information about each and every Html tag and it's attributes. If it encounters an unknown tag, it eliminates it. This means that it stumbles with every new Html tag in the future. You can define user defined tags but this is cumbersome and will be an eternal work that never ends! The last change in the code was 2009. This is a dead project.