In 2019, Mozilla implemented built-in CSS counter behavior for the ‘list-item’ keyword, which did not have a normative specification. They submitted a pull request for the HTML specification but did not follow through. Gecko had thus diverged in behavior, but there was interest from Chromium to also make this change, as it removes some of the rendering “magic” in HTML.
Our objective was to complete the specification and tests for how ‘list-item’ CSS counters work for HTML, ensure it is well tested and implementable in all browser engines.