Scoped Styles in HTML5
The `scoped` attribute on HTML5's `<style>` element limits CSS rules to only the parent element's subtree, enabling styled content to be syndicated across different pages or embedded as widgets without affecting the receiving document's styles. Although no browser supported it at the time of writing (with Chrome Canary beginning experimental support), the feature faced a significant adoption barrier because non-supporting browsers would apply scoped styles globally rather than ignoring them gracefully, making widespread use impractical until cross-browser support materialized. A jQuery polyfill existed as a workaround for most browsers, though the author questioned why the spec didn't create a new element type instead of an attribute for better backwards compatibility.