CSS Anchor Positioning in LayoutNG

The sources provide a comprehensive specification deep dive into CSS Anchor Positioning, a modern layout module designed to position elements like tooltips and popovers relative to an anchor without requiring JavaScript. Core mechanisms rely on defining the anchor using anchor-name and tethering the positioned element with position-anchor, allowing precise placement through the anchor() function and dynamic sizing via anchor-size(). The system addresses spatial constraints automatically using the Position Try mechanism, which applies ordered fallbacks (e.g., flip-block) to prevent overflow, supported by conditional visibility controls like position-visibility. A large portion of the text explains the technical implementation within the Chromium LayoutNG engine, detailing how it computes anchor coordinates and utilizes the compositor for high-performance scroll compensation. While the module is actively shipping in browsers, ongoing efforts focus on developing features like anchor-scope for better component isolation and Level 2 Anchor Queries for styling based on the active fallback position.