This implements the CSS @counter-style rule so that web authors can specify and use custom counter styles in list markers and CSS counters. This improves internationalization of the web.
This is a highly demanded CSS feature, especially by developers with needs in internationalization. The tracking bug (crbug.com/687225) has 40 stars, and already contains multiple detailed use cases of the feature.
This should greatly improve interoperability. The spec is already in Candidate Recommendation status and Firefox already shipped it in 2014, while no other browser has shipped it yet.