The sources provide an in-depth explanation of the Intersection Observer API within the Blink rendering engine, focusing on its architecture and implementation to improve web performance. The initial Intersection Observer v1 was designed to efficiently monitor the geometric visibility of DOM elements, replacing costly manual polling and reducing layout thrashing for common features like lazy loading. Furthermore, the documents detail Intersection Observer v2, an extension that adds the crucial ability to detect actual visibility, addressing security and anti-fraud concerns by checking for elements hidden by occlusion or transparency. Blink integrates this API into the frame lifecycle by using a central controller to coordinate checks after layout, ensuring updates are batched and asynchronous for smooth rendering.
