What this library cannot do

Publishing the limits is a differentiator, not a weakness. Every competitor hides them and users find out in production.

Want	Why CSS cannot	What Animatio ships
Cursor-following spotlight, magnetic pull	CSS has no access to pointer coordinates	an-spotlight-static and an-hover-tilt-grid (genuinely CSS-only, via hover zones), plus a 6-line feed that sets --an-mx/--an-my — the effect stays in our CSS
Text scramble	CSS cannot author text content	an-text-flip-chars — each glyph flips in place to reveal the final one
Per-character animation without spans	There is no ::nth-letter()	Split snippets + --an-i for the stagger
Velocity-reactive physics, collisions	No runtime state in CSS	linear() spring curves, which cover most of the feel
Particles, canvas, WebGL	A different rendering model	Nothing. Use three.js, and we will say so.
Scroll "once" in Firefox today	CSS cannot latch a scrubbed timeline	The tier ladder, plus an optional 12-line enhancer
SVG refraction in Safari	webkit #245510	an-glass plus an opt-in refract path

The once problem, in detail

animation-timeline: view() binds progress to scroll position. So:

• Back-and-forth is free. It is the default, not a feature.
• Play-once is the hard case. A scrubbed timeline cannot be latched in pure CSS — confirmed by the spec author.

Animatio exposes this as two class families rather than pretending one API does both: an-scrub-* follows the scrollbar, an-reveal fires on entry. an-reveal then resolves through three tiers, and the docs tell you which one you are on.

If you need true once in Firefox today, animatio/once.js is twelve lines of IntersectionObserver. It is never referenced by the CSS and nothing requires it. Honest framing beats a "CSS ONLY" claim that quietly is not.

Markup helpers, not CSS

Some effects need extra elements. They are marked ◑ throughout, and each ships a copy-paste snippet:

• an-glitch needs data-text duplicated for its two pseudo-layers
• an-text-split-* needs one span per character
• an-flip-card needs a front/back pair
• an-marquee needs the track duplicated for a seamless loop
• an-hover-tilt-grid needs nine hover zones

That is a markup helper, not CSS-only, and calling it anything else would be a lie you would discover at implementation time.