On-scroll reveal script (IntersectionObserver) driving the .is-visible hook

[jackgranatowski]

Idea

Ship a tiny front-end script that uses IntersectionObserver to add the framework's .is-visible class (or a data attribute) to elements as they enter the viewport — enabling "animate once when visible, stay visible" reveals that the pure-CSS framework intentionally doesn't provide.

Why

Scroll reveals are extremely common on marketing pages. The framework is zero-runtime-JS by design, so this belongs in the plugin. The CSS hook (.is-visible state) already exists.

Scope

• Small, dependency-free script, opt-in, honouring prefers-reduced-motion.
• data-* to skip/configure threshold + stagger per element.
• Enqueue only when the feature is enabled.

Acceptance

• Elements get .is-visible on first entry (no reversal on scroll-back), reduced-motion safe, opt-in