See https://github.com/w3c/csswg-drafts/issues/10577 for discussion on this. I'm hoping this gets eventually standardized but if not we can always undo this and use if() or what not once that's available. For now add an internal WPT reftest. Differential Revision: https://phabricator.services.mozilla.com/D249788
Common testing tools for mozilla codebase projects, test suite definitions for automated test runs, tests that don't fit anywhere else, and other fun stuff